mm: revert "vmscan: get_scan_ratio() cleanup"
[linux-2.6.git] / mm / ksm.c
index cf072c5..8cdfc2a 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
 #include <linux/wait.h>
 #include <linux/slab.h>
 #include <linux/rbtree.h>
+#include <linux/memory.h>
 #include <linux/mmu_notifier.h>
+#include <linux/swap.h>
 #include <linux/ksm.h>
 
 #include <asm/tlbflush.h>
+#include "internal.h"
 
 /*
  * A few notes about the KSM scanning process,
  * struct mm_slot - ksm information per mm that is being scanned
  * @link: link to the mm_slots hash list
  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
- * @rmap_list: head for this mm_slot's list of rmap_items
+ * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
  * @mm: the mm that this information is valid for
  */
 struct mm_slot {
        struct hlist_node link;
        struct list_head mm_list;
-       struct list_head rmap_list;
+       struct rmap_item *rmap_list;
        struct mm_struct *mm;
 };
 
@@ -92,7 +95,7 @@ struct mm_slot {
  * struct ksm_scan - cursor for scanning
  * @mm_slot: the current mm_slot we are scanning
  * @address: the next address inside that to be scanned
- * @rmap_item: the current rmap that we are scanning inside the rmap_list
+ * @rmap_list: link to the next rmap to be scanned in the rmap_list
  * @seqnr: count of completed full scans (needed when removing unstable node)
  *
  * There is only the one ksm_scan instance of this cursor structure.
@@ -100,37 +103,51 @@ struct mm_slot {
 struct ksm_scan {
        struct mm_slot *mm_slot;
        unsigned long address;
-       struct rmap_item *rmap_item;
+       struct rmap_item **rmap_list;
        unsigned long seqnr;
 };
 
 /**
+ * struct stable_node - node of the stable rbtree
+ * @node: rb node of this ksm page in the stable tree
+ * @hlist: hlist head of rmap_items using this ksm page
+ * @kpfn: page frame number of this ksm page
+ */
+struct stable_node {
+       struct rb_node node;
+       struct hlist_head hlist;
+       unsigned long kpfn;
+};
+
+/**
  * struct rmap_item - reverse mapping item for virtual addresses
- * @link: link into mm_slot's rmap_list (rmap_list is per mm)
+ * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
+ * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
  * @mm: the memory structure this rmap_item is pointing into
  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
  * @oldchecksum: previous checksum of the page at that virtual address
- * @node: rb_node of this rmap_item in either unstable or stable tree
- * @next: next rmap_item hanging off the same node of the stable tree
- * @prev: previous rmap_item hanging off the same node of the stable tree
+ * @node: rb node of this rmap_item in the unstable tree
+ * @head: pointer to stable_node heading this list in the stable tree
+ * @hlist: link into hlist of rmap_items hanging off that stable_node
  */
 struct rmap_item {
-       struct list_head link;
+       struct rmap_item *rmap_list;
+       struct anon_vma *anon_vma;      /* when stable */
        struct mm_struct *mm;
        unsigned long address;          /* + low bits used for flags below */
+       unsigned int oldchecksum;       /* when unstable */
        union {
-               unsigned int oldchecksum;               /* when unstable */
-               struct rmap_item *next;                 /* when stable */
-       };
-       union {
-               struct rb_node node;                    /* when tree node */
-               struct rmap_item *prev;                 /* in stable list */
+               struct rb_node node;    /* when node of unstable tree */
+               struct {                /* when listed from stable tree */
+                       struct stable_node *head;
+                       struct hlist_node hlist;
+               };
        };
 };
 
 #define SEQNR_MASK     0x0ff   /* low bits of unstable tree seqnr */
-#define NODE_FLAG      0x100   /* is a node of unstable or stable tree */
-#define STABLE_FLAG    0x200   /* is a node or list item of stable tree */
+#define UNSTABLE_FLAG  0x100   /* is a node of the unstable tree */
+#define STABLE_FLAG    0x200   /* is listed from the stable tree */
 
 /* The stable and unstable tree heads */
 static struct rb_root root_stable_tree = RB_ROOT;
@@ -147,27 +164,31 @@ static struct ksm_scan ksm_scan = {
 };
 
 static struct kmem_cache *rmap_item_cache;
+static struct kmem_cache *stable_node_cache;
 static struct kmem_cache *mm_slot_cache;
 
 /* The number of nodes in the stable tree */
-static unsigned long ksm_kernel_pages_allocated;
-
-/* The number of page slots sharing those nodes */
 static unsigned long ksm_pages_shared;
 
-/* Limit on the number of unswappable pages used */
-static unsigned long ksm_max_kernel_pages;
+/* The number of page slots additionally sharing those nodes */
+static unsigned long ksm_pages_sharing;
+
+/* The number of nodes in the unstable tree */
+static unsigned long ksm_pages_unshared;
+
+/* The number of rmap_items in use: to calculate pages_volatile */
+static unsigned long ksm_rmap_items;
 
 /* Number of pages ksmd should scan in one batch */
-static unsigned int ksm_thread_pages_to_scan;
+static unsigned int ksm_thread_pages_to_scan = 100;
 
 /* Milliseconds ksmd should sleep between batches */
-static unsigned int ksm_thread_sleep_millisecs;
+static unsigned int ksm_thread_sleep_millisecs = 20;
 
 #define KSM_RUN_STOP   0
 #define KSM_RUN_MERGE  1
 #define KSM_RUN_UNMERGE        2
-static unsigned int ksm_run;
+static unsigned int ksm_run = KSM_RUN_STOP;
 
 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
 static DEFINE_MUTEX(ksm_thread_mutex);
@@ -183,13 +204,19 @@ static int __init ksm_slab_init(void)
        if (!rmap_item_cache)
                goto out;
 
+       stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
+       if (!stable_node_cache)
+               goto out_free1;
+
        mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
        if (!mm_slot_cache)
-               goto out_free;
+               goto out_free2;
 
        return 0;
 
-out_free:
+out_free2:
+       kmem_cache_destroy(stable_node_cache);
+out_free1:
        kmem_cache_destroy(rmap_item_cache);
 out:
        return -ENOMEM;
@@ -198,21 +225,38 @@ out:
 static void __init ksm_slab_free(void)
 {
        kmem_cache_destroy(mm_slot_cache);
+       kmem_cache_destroy(stable_node_cache);
        kmem_cache_destroy(rmap_item_cache);
        mm_slot_cache = NULL;
 }
 
 static inline struct rmap_item *alloc_rmap_item(void)
 {
-       return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
+       struct rmap_item *rmap_item;
+
+       rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
+       if (rmap_item)
+               ksm_rmap_items++;
+       return rmap_item;
 }
 
 static inline void free_rmap_item(struct rmap_item *rmap_item)
 {
+       ksm_rmap_items--;
        rmap_item->mm = NULL;   /* debug safety */
        kmem_cache_free(rmap_item_cache, rmap_item);
 }
 
+static inline struct stable_node *alloc_stable_node(void)
+{
+       return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
+}
+
+static inline void free_stable_node(struct stable_node *stable_node)
+{
+       kmem_cache_free(stable_node_cache, stable_node);
+}
+
 static inline struct mm_slot *alloc_mm_slot(void)
 {
        if (!mm_slot_cache)     /* initialization failed */
@@ -262,7 +306,6 @@ static void insert_to_mm_slots_hash(struct mm_struct *mm,
        bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
                                % MM_SLOTS_HASH_HEADS];
        mm_slot->mm = mm;
-       INIT_LIST_HEAD(&mm_slot->rmap_list);
        hlist_add_head(&mm_slot->link, bucket);
 }
 
@@ -271,6 +314,38 @@ static inline int in_stable_tree(struct rmap_item *rmap_item)
        return rmap_item->address & STABLE_FLAG;
 }
 
+static void hold_anon_vma(struct rmap_item *rmap_item,
+                         struct anon_vma *anon_vma)
+{
+       rmap_item->anon_vma = anon_vma;
+       atomic_inc(&anon_vma->ksm_refcount);
+}
+
+static void drop_anon_vma(struct rmap_item *rmap_item)
+{
+       struct anon_vma *anon_vma = rmap_item->anon_vma;
+
+       if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) {
+               int empty = list_empty(&anon_vma->head);
+               spin_unlock(&anon_vma->lock);
+               if (empty)
+                       anon_vma_free(anon_vma);
+       }
+}
+
+/*
+ * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
+ * page tables after it has passed through ksm_exit() - which, if necessary,
+ * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
+ * a special flag: they can just back out as soon as mm_users goes to zero.
+ * ksm_test_exit() is used throughout to make this test for exit: in some
+ * places for correctness, in some places just to avoid unnecessary work.
+ */
+static inline bool ksm_test_exit(struct mm_struct *mm)
+{
+       return atomic_read(&mm->mm_users) == 0;
+}
+
 /*
  * We use break_ksm to break COW on a ksm page: it's a stripped down
  *
@@ -282,10 +357,10 @@ static inline int in_stable_tree(struct rmap_item *rmap_item)
  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
  */
-static void break_ksm(struct vm_area_struct *vma, unsigned long addr)
+static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 {
        struct page *page;
-       int ret;
+       int ret = 0;
 
        do {
                cond_resched();
@@ -298,27 +373,60 @@ static void break_ksm(struct vm_area_struct *vma, unsigned long addr)
                else
                        ret = VM_FAULT_WRITE;
                put_page(page);
-       } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS)));
-
-       /* Which leaves us looping there if VM_FAULT_OOM: hmmm... */
+       } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
+       /*
+        * We must loop because handle_mm_fault() may back out if there's
+        * any difficulty e.g. if pte accessed bit gets updated concurrently.
+        *
+        * VM_FAULT_WRITE is what we have been hoping for: it indicates that
+        * COW has been broken, even if the vma does not permit VM_WRITE;
+        * but note that a concurrent fault might break PageKsm for us.
+        *
+        * VM_FAULT_SIGBUS could occur if we race with truncation of the
+        * backing file, which also invalidates anonymous pages: that's
+        * okay, that truncation will have unmapped the PageKsm for us.
+        *
+        * VM_FAULT_OOM: at the time of writing (late July 2009), setting
+        * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
+        * current task has TIF_MEMDIE set, and will be OOM killed on return
+        * to user; and ksmd, having no mm, would never be chosen for that.
+        *
+        * But if the mm is in a limited mem_cgroup, then the fault may fail
+        * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
+        * even ksmd can fail in this way - though it's usually breaking ksm
+        * just to undo a merge it made a moment before, so unlikely to oom.
+        *
+        * That's a pity: we might therefore have more kernel pages allocated
+        * than we're counting as nodes in the stable tree; but ksm_do_scan
+        * will retry to break_cow on each pass, so should recover the page
+        * in due course.  The important thing is to not let VM_MERGEABLE
+        * be cleared while any such pages might remain in the area.
+        */
+       return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
 }
 
-static void __break_cow(struct mm_struct *mm, unsigned long addr)
+static void break_cow(struct rmap_item *rmap_item)
 {
+       struct mm_struct *mm = rmap_item->mm;
+       unsigned long addr = rmap_item->address;
        struct vm_area_struct *vma;
 
+       /*
+        * It is not an accident that whenever we want to break COW
+        * to undo, we also need to drop a reference to the anon_vma.
+        */
+       drop_anon_vma(rmap_item);
+
+       down_read(&mm->mmap_sem);
+       if (ksm_test_exit(mm))
+               goto out;
        vma = find_vma(mm, addr);
        if (!vma || vma->vm_start > addr)
-               return;
+               goto out;
        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
-               return;
+               goto out;
        break_ksm(vma, addr);
-}
-
-static void break_cow(struct mm_struct *mm, unsigned long addr)
-{
-       down_read(&mm->mmap_sem);
-       __break_cow(mm, addr);
+out:
        up_read(&mm->mmap_sem);
 }
 
@@ -330,6 +438,8 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item)
        struct page *page;
 
        down_read(&mm->mmap_sem);
+       if (ksm_test_exit(mm))
+               goto out;
        vma = find_vma(mm, addr);
        if (!vma || vma->vm_start > addr)
                goto out;
@@ -350,21 +460,77 @@ out:              page = NULL;
        return page;
 }
 
+static void remove_node_from_stable_tree(struct stable_node *stable_node)
+{
+       struct rmap_item *rmap_item;
+       struct hlist_node *hlist;
+
+       hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
+               if (rmap_item->hlist.next)
+                       ksm_pages_sharing--;
+               else
+                       ksm_pages_shared--;
+               drop_anon_vma(rmap_item);
+               rmap_item->address &= PAGE_MASK;
+               cond_resched();
+       }
+
+       rb_erase(&stable_node->node, &root_stable_tree);
+       free_stable_node(stable_node);
+}
+
 /*
- * get_ksm_page: checks if the page at the virtual address in rmap_item
- * is still PageKsm, in which case we can trust the content of the page,
- * and it returns the gotten page; but NULL if the page has been zapped.
+ * get_ksm_page: checks if the page indicated by the stable node
+ * is still its ksm page, despite having held no reference to it.
+ * In which case we can trust the content of the page, and it
+ * returns the gotten page; but if the page has now been zapped,
+ * remove the stale node from the stable tree and return NULL.
+ *
+ * You would expect the stable_node to hold a reference to the ksm page.
+ * But if it increments the page's count, swapping out has to wait for
+ * ksmd to come around again before it can free the page, which may take
+ * seconds or even minutes: much too unresponsive.  So instead we use a
+ * "keyhole reference": access to the ksm page from the stable node peeps
+ * out through its keyhole to see if that page still holds the right key,
+ * pointing back to this stable node.  This relies on freeing a PageAnon
+ * page to reset its page->mapping to NULL, and relies on no other use of
+ * a page to put something that might look like our key in page->mapping.
+ *
+ * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
+ * but this is different - made simpler by ksm_thread_mutex being held, but
+ * interesting for assuming that no other use of the struct page could ever
+ * put our expected_mapping into page->mapping (or a field of the union which
+ * coincides with page->mapping).  The RCU calls are not for KSM at all, but
+ * to keep the page_count protocol described with page_cache_get_speculative.
+ *
+ * Note: it is possible that get_ksm_page() will return NULL one moment,
+ * then page the next, if the page is in between page_freeze_refs() and
+ * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
+ * is on its way to being freed; but it is an anomaly to bear in mind.
  */
-static struct page *get_ksm_page(struct rmap_item *rmap_item)
+static struct page *get_ksm_page(struct stable_node *stable_node)
 {
        struct page *page;
-
-       page = get_mergeable_page(rmap_item);
-       if (page && !PageKsm(page)) {
+       void *expected_mapping;
+
+       page = pfn_to_page(stable_node->kpfn);
+       expected_mapping = (void *)stable_node +
+                               (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
+       rcu_read_lock();
+       if (page->mapping != expected_mapping)
+               goto stale;
+       if (!get_page_unless_zero(page))
+               goto stale;
+       if (page->mapping != expected_mapping) {
                put_page(page);
-               page = NULL;
+               goto stale;
        }
+       rcu_read_unlock();
        return page;
+stale:
+       rcu_read_unlock();
+       remove_node_from_stable_tree(stable_node);
+       return NULL;
 }
 
 /*
@@ -373,79 +539,56 @@ static struct page *get_ksm_page(struct rmap_item *rmap_item)
  */
 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 {
-       if (in_stable_tree(rmap_item)) {
-               struct rmap_item *next_item = rmap_item->next;
-
-               if (rmap_item->address & NODE_FLAG) {
-                       if (next_item) {
-                               rb_replace_node(&rmap_item->node,
-                                               &next_item->node,
-                                               &root_stable_tree);
-                               next_item->address |= NODE_FLAG;
-                       } else {
-                               rb_erase(&rmap_item->node, &root_stable_tree);
-                               ksm_kernel_pages_allocated--;
-                       }
-               } else {
-                       struct rmap_item *prev_item = rmap_item->prev;
+       if (rmap_item->address & STABLE_FLAG) {
+               struct stable_node *stable_node;
+               struct page *page;
 
-                       BUG_ON(prev_item->next != rmap_item);
-                       prev_item->next = next_item;
-                       if (next_item) {
-                               BUG_ON(next_item->prev != rmap_item);
-                               next_item->prev = rmap_item->prev;
-                       }
-               }
+               stable_node = rmap_item->head;
+               page = get_ksm_page(stable_node);
+               if (!page)
+                       goto out;
 
-               rmap_item->next = NULL;
-               ksm_pages_shared--;
+               lock_page(page);
+               hlist_del(&rmap_item->hlist);
+               unlock_page(page);
+               put_page(page);
 
-       } else if (rmap_item->address & NODE_FLAG) {
+               if (stable_node->hlist.first)
+                       ksm_pages_sharing--;
+               else
+                       ksm_pages_shared--;
+
+               drop_anon_vma(rmap_item);
+               rmap_item->address &= PAGE_MASK;
+
+       } else if (rmap_item->address & UNSTABLE_FLAG) {
                unsigned char age;
                /*
-                * ksm_thread can and must skip the rb_erase, because
+                * Usually ksmd can and must skip the rb_erase, because
                 * root_unstable_tree was already reset to RB_ROOT.
-                * But __ksm_exit has to be careful: do the rb_erase
-                * if it's interrupting a scan, and this rmap_item was
-                * inserted by this scan rather than left from before.
-                *
-                * Because of the case in which remove_mm_from_lists
-                * increments seqnr before removing rmaps, unstable_nr
-                * may even be 2 behind seqnr, but should never be
-                * further behind.  Yes, I did have trouble with this!
+                * But be careful when an mm is exiting: do the rb_erase
+                * if this rmap_item was inserted by this scan, rather
+                * than left over from before.
                 */
                age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
-               BUG_ON(age > 2);
+               BUG_ON(age > 1);
                if (!age)
                        rb_erase(&rmap_item->node, &root_unstable_tree);
-       }
-
-       rmap_item->address &= PAGE_MASK;
-
-       cond_resched();         /* we're called from many long loops */
-}
-
-static void remove_all_slot_rmap_items(struct mm_slot *mm_slot)
-{
-       struct rmap_item *rmap_item, *node;
 
-       list_for_each_entry_safe(rmap_item, node, &mm_slot->rmap_list, link) {
-               remove_rmap_item_from_tree(rmap_item);
-               list_del(&rmap_item->link);
-               free_rmap_item(rmap_item);
+               ksm_pages_unshared--;
+               rmap_item->address &= PAGE_MASK;
        }
+out:
+       cond_resched();         /* we're called from many long loops */
 }
 
 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
-                                      struct list_head *cur)
+                                      struct rmap_item **rmap_list)
 {
-       struct rmap_item *rmap_item;
-
-       while (cur != &mm_slot->rmap_list) {
-               rmap_item = list_entry(cur, struct rmap_item, link);
-               cur = cur->next;
+       while (*rmap_list) {
+               struct rmap_item *rmap_item = *rmap_list;
+               *rmap_list = rmap_item->rmap_list;
                remove_rmap_item_from_tree(rmap_item);
-               list_del(&rmap_item->link);
                free_rmap_item(rmap_item);
        }
 }
@@ -457,72 +600,91 @@ static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
  * rmap_items from parent to child at fork time (so as not to waste time
  * if exit comes before the next scan reaches it).
+ *
+ * Similarly, although we'd like to remove rmap_items (so updating counts
+ * and freeing memory) when unmerging an area, it's easier to leave that
+ * to the next pass of ksmd - consider, for example, how ksmd might be
+ * in cmp_and_merge_page on one of the rmap_items we would be removing.
  */
-static void unmerge_ksm_pages(struct vm_area_struct *vma,
-                             unsigned long start, unsigned long end)
+static int unmerge_ksm_pages(struct vm_area_struct *vma,
+                            unsigned long start, unsigned long end)
 {
        unsigned long addr;
+       int err = 0;
 
-       for (addr = start; addr < end; addr += PAGE_SIZE)
-               break_ksm(vma, addr);
+       for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
+               if (ksm_test_exit(vma->vm_mm))
+                       break;
+               if (signal_pending(current))
+                       err = -ERESTARTSYS;
+               else
+                       err = break_ksm(vma, addr);
+       }
+       return err;
 }
 
-static void unmerge_and_remove_all_rmap_items(void)
+#ifdef CONFIG_SYSFS
+/*
+ * Only called through the sysfs control interface:
+ */
+static int unmerge_and_remove_all_rmap_items(void)
 {
        struct mm_slot *mm_slot;
        struct mm_struct *mm;
        struct vm_area_struct *vma;
+       int err = 0;
+
+       spin_lock(&ksm_mmlist_lock);
+       ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
+                                               struct mm_slot, mm_list);
+       spin_unlock(&ksm_mmlist_lock);
 
-       list_for_each_entry(mm_slot, &ksm_mm_head.mm_list, mm_list) {
+       for (mm_slot = ksm_scan.mm_slot;
+                       mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
                mm = mm_slot->mm;
                down_read(&mm->mmap_sem);
                for (vma = mm->mmap; vma; vma = vma->vm_next) {
+                       if (ksm_test_exit(mm))
+                               break;
                        if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
                                continue;
-                       unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end);
+                       err = unmerge_ksm_pages(vma,
+                                               vma->vm_start, vma->vm_end);
+                       if (err)
+                               goto error;
                }
-               remove_all_slot_rmap_items(mm_slot);
-               up_read(&mm->mmap_sem);
-       }
 
-       spin_lock(&ksm_mmlist_lock);
-       if (ksm_scan.mm_slot != &ksm_mm_head) {
-               ksm_scan.mm_slot = &ksm_mm_head;
-               ksm_scan.seqnr++;
+               remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
+
+               spin_lock(&ksm_mmlist_lock);
+               ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
+                                               struct mm_slot, mm_list);
+               if (ksm_test_exit(mm)) {
+                       hlist_del(&mm_slot->link);
+                       list_del(&mm_slot->mm_list);
+                       spin_unlock(&ksm_mmlist_lock);
+
+                       free_mm_slot(mm_slot);
+                       clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+                       up_read(&mm->mmap_sem);
+                       mmdrop(mm);
+               } else {
+                       spin_unlock(&ksm_mmlist_lock);
+                       up_read(&mm->mmap_sem);
+               }
        }
-       spin_unlock(&ksm_mmlist_lock);
-}
 
-static void remove_mm_from_lists(struct mm_struct *mm)
-{
-       struct mm_slot *mm_slot;
+       ksm_scan.seqnr = 0;
+       return 0;
 
+error:
+       up_read(&mm->mmap_sem);
        spin_lock(&ksm_mmlist_lock);
-       mm_slot = get_mm_slot(mm);
-
-       /*
-        * This mm_slot is always at the scanning cursor when we're
-        * called from scan_get_next_rmap_item; but it's a special
-        * case when we're called from __ksm_exit.
-        */
-       if (ksm_scan.mm_slot == mm_slot) {
-               ksm_scan.mm_slot = list_entry(
-                       mm_slot->mm_list.next, struct mm_slot, mm_list);
-               ksm_scan.address = 0;
-               ksm_scan.rmap_item = list_entry(
-                       &ksm_scan.mm_slot->rmap_list, struct rmap_item, link);
-               if (ksm_scan.mm_slot == &ksm_mm_head)
-                       ksm_scan.seqnr++;
-       }
-
-       hlist_del(&mm_slot->link);
-       list_del(&mm_slot->mm_list);
+       ksm_scan.mm_slot = &ksm_mm_head;
        spin_unlock(&ksm_mmlist_lock);
-
-       remove_all_slot_rmap_items(mm_slot);
-       free_mm_slot(mm_slot);
-       clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+       return err;
 }
+#endif /* CONFIG_SYSFS */
 
 static u32 calc_checksum(struct page *page)
 {
@@ -588,8 +750,8 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
                 * Check that no O_DIRECT or similar I/O is in progress on the
                 * page
                 */
-               if ((page_mapcount(page) + 2 + swapped) != page_count(page)) {
-                       set_pte_at_notify(mm, addr, ptep, entry);
+               if (page_mapcount(page) + 1 + swapped != page_count(page)) {
+                       set_pte_at(mm, addr, ptep, entry);
                        goto out_unlock;
                }
                entry = pte_wrprotect(entry);
@@ -606,15 +768,15 @@ out:
 
 /**
  * replace_page - replace page in vma by new ksm page
- * @vma:      vma that holds the pte pointing to oldpage
- * @oldpage:  the page we are replacing by newpage
- * @newpage:  the ksm page we replace oldpage by
+ * @vma:      vma that holds the pte pointing to page
+ * @page:     the page we are replacing by kpage
+ * @kpage:    the ksm page we replace page by
  * @orig_pte: the original value of the pte
  *
  * Returns 0 on success, -EFAULT on failure.
  */
-static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
-                       struct page *newpage, pte_t orig_pte)
+static int replace_page(struct vm_area_struct *vma, struct page *page,
+                       struct page *kpage, pte_t orig_pte)
 {
        struct mm_struct *mm = vma->vm_mm;
        pgd_t *pgd;
@@ -623,12 +785,9 @@ static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
        pte_t *ptep;
        spinlock_t *ptl;
        unsigned long addr;
-       pgprot_t prot;
        int err = -EFAULT;
 
-       prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE);
-
-       addr = page_address_in_vma(oldpage, vma);
+       addr = page_address_in_vma(page, vma);
        if (addr == -EFAULT)
                goto out;
 
@@ -650,15 +809,15 @@ static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
                goto out;
        }
 
-       get_page(newpage);
-       page_add_ksm_rmap(newpage);
+       get_page(kpage);
+       page_add_anon_rmap(kpage, vma, addr);
 
        flush_cache_page(vma, addr, pte_pfn(*ptep));
        ptep_clear_flush(vma, addr, ptep);
-       set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot));
+       set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 
-       page_remove_rmap(oldpage);
-       put_page(oldpage);
+       page_remove_rmap(page);
+       put_page(page);
 
        pte_unmap_unlock(ptep, ptl);
        err = 0;
@@ -668,32 +827,27 @@ out:
 
 /*
  * try_to_merge_one_page - take two pages and merge them into one
- * @vma: the vma that hold the pte pointing into oldpage
- * @oldpage: the page that we want to replace with newpage
- * @newpage: the page that we want to map instead of oldpage
- *
- * Note:
- * oldpage should be a PageAnon page, while newpage should be a PageKsm page,
- * or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm.
+ * @vma: the vma that holds the pte pointing to page
+ * @page: the PageAnon page that we want to replace with kpage
+ * @kpage: the PageKsm page that we want to map instead of page,
+ *         or NULL the first time when we want to use page as kpage.
  *
  * This function returns 0 if the pages were merged, -EFAULT otherwise.
  */
 static int try_to_merge_one_page(struct vm_area_struct *vma,
-                                struct page *oldpage,
-                                struct page *newpage)
+                                struct page *page, struct page *kpage)
 {
        pte_t orig_pte = __pte(0);
        int err = -EFAULT;
 
+       if (page == kpage)                      /* ksm page forked */
+               return 0;
+
        if (!(vma->vm_flags & VM_MERGEABLE))
                goto out;
-
-       if (!PageAnon(oldpage))
+       if (!PageAnon(page))
                goto out;
 
-       get_page(newpage);
-       get_page(oldpage);
-
        /*
         * We need the page lock to read a stable PageSwapCache in
         * write_protect_page().  We use trylock_page() instead of
@@ -701,175 +855,145 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
         * prefer to continue scanning and merging different pages,
         * then come back to this page when it is unlocked.
         */
-       if (!trylock_page(oldpage))
-               goto out_putpage;
+       if (!trylock_page(page))
+               goto out;
        /*
         * If this anonymous page is mapped only here, its pte may need
         * to be write-protected.  If it's mapped elsewhere, all of its
         * ptes are necessarily already write-protected.  But in either
         * case, we need to lock and check page_count is not raised.
         */
-       if (write_protect_page(vma, oldpage, &orig_pte)) {
-               unlock_page(oldpage);
-               goto out_putpage;
+       if (write_protect_page(vma, page, &orig_pte) == 0) {
+               if (!kpage) {
+                       /*
+                        * While we hold page lock, upgrade page from
+                        * PageAnon+anon_vma to PageKsm+NULL stable_node:
+                        * stable_tree_insert() will update stable_node.
+                        */
+                       set_page_stable_node(page, NULL);
+                       mark_page_accessed(page);
+                       err = 0;
+               } else if (pages_identical(page, kpage))
+                       err = replace_page(vma, page, kpage, orig_pte);
        }
-       unlock_page(oldpage);
 
-       if (pages_identical(oldpage, newpage))
-               err = replace_page(vma, oldpage, newpage, orig_pte);
+       if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
+               munlock_vma_page(page);
+               if (!PageMlocked(kpage)) {
+                       unlock_page(page);
+                       lock_page(kpage);
+                       mlock_vma_page(kpage);
+                       page = kpage;           /* for final unlock */
+               }
+       }
 
-out_putpage:
-       put_page(oldpage);
-       put_page(newpage);
+       unlock_page(page);
 out:
        return err;
 }
 
 /*
- * try_to_merge_two_pages - take two identical pages and prepare them
- * to be merged into one page.
- *
- * This function returns 0 if we successfully mapped two identical pages
- * into one page, -EFAULT otherwise.
+ * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
+ * but no new kernel page is allocated: kpage must already be a ksm page.
  *
- * Note that this function allocates a new kernel page: if one of the pages
- * is already a ksm page, try_to_merge_with_ksm_page should be used.
+ * This function returns 0 if the pages were merged, -EFAULT otherwise.
  */
-static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
-                                 struct page *page1, struct mm_struct *mm2,
-                                 unsigned long addr2, struct page *page2)
+static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
+                                     struct page *page, struct page *kpage)
 {
+       struct mm_struct *mm = rmap_item->mm;
        struct vm_area_struct *vma;
-       struct page *kpage;
        int err = -EFAULT;
 
-       /*
-        * The number of nodes in the stable tree
-        * is the number of kernel pages that we hold.
-        */
-       if (ksm_max_kernel_pages &&
-           ksm_max_kernel_pages <= ksm_kernel_pages_allocated)
-               return err;
-
-       kpage = alloc_page(GFP_HIGHUSER);
-       if (!kpage)
-               return err;
-
-       down_read(&mm1->mmap_sem);
-       vma = find_vma(mm1, addr1);
-       if (!vma || vma->vm_start > addr1) {
-               put_page(kpage);
-               up_read(&mm1->mmap_sem);
-               return err;
-       }
-
-       copy_user_highpage(kpage, page1, addr1, vma);
-       err = try_to_merge_one_page(vma, page1, kpage);
-       up_read(&mm1->mmap_sem);
-
-       if (!err) {
-               down_read(&mm2->mmap_sem);
-               vma = find_vma(mm2, addr2);
-               if (!vma || vma->vm_start > addr2) {
-                       put_page(kpage);
-                       up_read(&mm2->mmap_sem);
-                       break_cow(mm1, addr1);
-                       return -EFAULT;
-               }
-
-               err = try_to_merge_one_page(vma, page2, kpage);
-               up_read(&mm2->mmap_sem);
+       down_read(&mm->mmap_sem);
+       if (ksm_test_exit(mm))
+               goto out;
+       vma = find_vma(mm, rmap_item->address);
+       if (!vma || vma->vm_start > rmap_item->address)
+               goto out;
 
-               /*
-                * If the second try_to_merge_one_page failed, we have a
-                * ksm page with just one pte pointing to it, so break it.
-                */
-               if (err)
-                       break_cow(mm1, addr1);
-               else
-                       ksm_pages_shared += 2;
-       }
+       err = try_to_merge_one_page(vma, page, kpage);
+       if (err)
+               goto out;
 
-       put_page(kpage);
+       /* Must get reference to anon_vma while still holding mmap_sem */
+       hold_anon_vma(rmap_item, vma->anon_vma);
+out:
+       up_read(&mm->mmap_sem);
        return err;
 }
 
 /*
- * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
- * but no new kernel page is allocated: kpage must already be a ksm page.
+ * try_to_merge_two_pages - take two identical pages and prepare them
+ * to be merged into one page.
+ *
+ * This function returns the kpage if we successfully merged two identical
+ * pages into one ksm page, NULL otherwise.
+ *
+ * Note that this function upgrades page to ksm page: if one of the pages
+ * is already a ksm page, try_to_merge_with_ksm_page should be used.
  */
-static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
-                                     unsigned long addr1,
-                                     struct page *page1,
-                                     struct page *kpage)
+static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
+                                          struct page *page,
+                                          struct rmap_item *tree_rmap_item,
+                                          struct page *tree_page)
 {
-       struct vm_area_struct *vma;
-       int err = -EFAULT;
+       int err;
 
-       down_read(&mm1->mmap_sem);
-       vma = find_vma(mm1, addr1);
-       if (!vma || vma->vm_start > addr1) {
-               up_read(&mm1->mmap_sem);
-               return err;
+       err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
+       if (!err) {
+               err = try_to_merge_with_ksm_page(tree_rmap_item,
+                                                       tree_page, page);
+               /*
+                * If that fails, we have a ksm page with only one pte
+                * pointing to it: so break it.
+                */
+               if (err)
+                       break_cow(rmap_item);
        }
-
-       err = try_to_merge_one_page(vma, page1, kpage);
-       up_read(&mm1->mmap_sem);
-
-       if (!err)
-               ksm_pages_shared++;
-
-       return err;
+       return err ? NULL : page;
 }
 
 /*
- * stable_tree_search - search page inside the stable tree
- * @page: the page that we are searching identical pages to.
- * @page2: pointer into identical page that we are holding inside the stable
- *        tree that we have found.
- * @rmap_item: the reverse mapping item
+ * stable_tree_search - search for page inside the stable tree
  *
  * This function checks if there is a page inside the stable tree
  * with identical content to the page that we are scanning right now.
  *
- * This function return rmap_item pointer to the identical item if found,
+ * This function returns the stable tree node of identical content if found,
  * NULL otherwise.
  */
-static struct rmap_item *stable_tree_search(struct page *page,
-                                           struct page **page2,
-                                           struct rmap_item *rmap_item)
+static struct page *stable_tree_search(struct page *page)
 {
        struct rb_node *node = root_stable_tree.rb_node;
+       struct stable_node *stable_node;
+
+       stable_node = page_stable_node(page);
+       if (stable_node) {                      /* ksm page forked */
+               get_page(page);
+               return page;
+       }
 
        while (node) {
-               struct rmap_item *tree_rmap_item, *next_rmap_item;
+               struct page *tree_page;
                int ret;
 
-               tree_rmap_item = rb_entry(node, struct rmap_item, node);
-               while (tree_rmap_item) {
-                       BUG_ON(!in_stable_tree(tree_rmap_item));
-                       cond_resched();
-                       page2[0] = get_ksm_page(tree_rmap_item);
-                       if (page2[0])
-                               break;
-                       next_rmap_item = tree_rmap_item->next;
-                       remove_rmap_item_from_tree(tree_rmap_item);
-                       tree_rmap_item = next_rmap_item;
-               }
-               if (!tree_rmap_item)
+               cond_resched();
+               stable_node = rb_entry(node, struct stable_node, node);
+               tree_page = get_ksm_page(stable_node);
+               if (!tree_page)
                        return NULL;
 
-               ret = memcmp_pages(page, page2[0]);
+               ret = memcmp_pages(page, tree_page);
 
                if (ret < 0) {
-                       put_page(page2[0]);
+                       put_page(tree_page);
                        node = node->rb_left;
                } else if (ret > 0) {
-                       put_page(page2[0]);
+                       put_page(tree_page);
                        node = node->rb_right;
-               } else {
-                       return tree_rmap_item;
-               }
+               } else
+                       return tree_page;
        }
 
        return NULL;
@@ -879,38 +1003,26 @@ static struct rmap_item *stable_tree_search(struct page *page,
  * stable_tree_insert - insert rmap_item pointing to new ksm page
  * into the stable tree.
  *
- * @page: the page that we are searching identical page to inside the stable
- *       tree.
- * @rmap_item: pointer to the reverse mapping item.
- *
- * This function returns rmap_item if success, NULL otherwise.
+ * This function returns the stable tree node just allocated on success,
+ * NULL otherwise.
  */
-static struct rmap_item *stable_tree_insert(struct page *page,
-                                           struct rmap_item *rmap_item)
+static struct stable_node *stable_tree_insert(struct page *kpage)
 {
        struct rb_node **new = &root_stable_tree.rb_node;
        struct rb_node *parent = NULL;
+       struct stable_node *stable_node;
 
        while (*new) {
-               struct rmap_item *tree_rmap_item, *next_rmap_item;
                struct page *tree_page;
                int ret;
 
-               tree_rmap_item = rb_entry(*new, struct rmap_item, node);
-               while (tree_rmap_item) {
-                       BUG_ON(!in_stable_tree(tree_rmap_item));
-                       cond_resched();
-                       tree_page = get_ksm_page(tree_rmap_item);
-                       if (tree_page)
-                               break;
-                       next_rmap_item = tree_rmap_item->next;
-                       remove_rmap_item_from_tree(tree_rmap_item);
-                       tree_rmap_item = next_rmap_item;
-               }
-               if (!tree_rmap_item)
+               cond_resched();
+               stable_node = rb_entry(*new, struct stable_node, node);
+               tree_page = get_ksm_page(stable_node);
+               if (!tree_page)
                        return NULL;
 
-               ret = memcmp_pages(page, tree_page);
+               ret = memcmp_pages(kpage, tree_page);
                put_page(tree_page);
 
                parent = *new;
@@ -928,23 +1040,24 @@ static struct rmap_item *stable_tree_insert(struct page *page,
                }
        }
 
-       ksm_kernel_pages_allocated++;
+       stable_node = alloc_stable_node();
+       if (!stable_node)
+               return NULL;
 
-       rmap_item->address |= NODE_FLAG | STABLE_FLAG;
-       rmap_item->next = NULL;
-       rb_link_node(&rmap_item->node, parent, new);
-       rb_insert_color(&rmap_item->node, &root_stable_tree);
+       rb_link_node(&stable_node->node, parent, new);
+       rb_insert_color(&stable_node->node, &root_stable_tree);
 
-       return rmap_item;
+       INIT_HLIST_HEAD(&stable_node->hlist);
+
+       stable_node->kpfn = page_to_pfn(kpage);
+       set_page_stable_node(kpage, stable_node);
+
+       return stable_node;
 }
 
 /*
- * unstable_tree_search_insert - search and insert items into the unstable tree.
- *
- * @page: the page that we are going to search for identical page or to insert
- *       into the unstable tree
- * @page2: pointer into identical page that was found inside the unstable tree
- * @rmap_item: the reverse mapping item of page
+ * unstable_tree_search_insert - search for identical page,
+ * else insert rmap_item into the unstable tree.
  *
  * This function searches for a page in the unstable tree identical to the
  * page currently being scanned; and if no identical page is found in the
@@ -956,50 +1069,55 @@ static struct rmap_item *stable_tree_insert(struct page *page,
  * This function does both searching and inserting, because they share
  * the same walking algorithm in an rbtree.
  */
-static struct rmap_item *unstable_tree_search_insert(struct page *page,
-                                               struct page **page2,
-                                               struct rmap_item *rmap_item)
+static
+struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
+                                             struct page *page,
+                                             struct page **tree_pagep)
+
 {
        struct rb_node **new = &root_unstable_tree.rb_node;
        struct rb_node *parent = NULL;
 
        while (*new) {
                struct rmap_item *tree_rmap_item;
+               struct page *tree_page;
                int ret;
 
+               cond_resched();
                tree_rmap_item = rb_entry(*new, struct rmap_item, node);
-               page2[0] = get_mergeable_page(tree_rmap_item);
-               if (!page2[0])
+               tree_page = get_mergeable_page(tree_rmap_item);
+               if (!tree_page)
                        return NULL;
 
                /*
-                * Don't substitute an unswappable ksm page
-                * just for one good swappable forked page.
+                * Don't substitute a ksm page for a forked page.
                 */
-               if (page == page2[0]) {
-                       put_page(page2[0]);
+               if (page == tree_page) {
+                       put_page(tree_page);
                        return NULL;
                }
 
-               ret = memcmp_pages(page, page2[0]);
+               ret = memcmp_pages(page, tree_page);
 
                parent = *new;
                if (ret < 0) {
-                       put_page(page2[0]);
+                       put_page(tree_page);
                        new = &parent->rb_left;
                } else if (ret > 0) {
-                       put_page(page2[0]);
+                       put_page(tree_page);
                        new = &parent->rb_right;
                } else {
+                       *tree_pagep = tree_page;
                        return tree_rmap_item;
                }
        }
 
-       rmap_item->address |= NODE_FLAG;
+       rmap_item->address |= UNSTABLE_FLAG;
        rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
        rb_link_node(&rmap_item->node, parent, new);
        rb_insert_color(&rmap_item->node, &root_unstable_tree);
 
+       ksm_pages_unshared++;
        return NULL;
 }
 
@@ -1009,71 +1127,60 @@ static struct rmap_item *unstable_tree_search_insert(struct page *page,
  * the same ksm page.
  */
 static void stable_tree_append(struct rmap_item *rmap_item,
-                              struct rmap_item *tree_rmap_item)
+                              struct stable_node *stable_node)
 {
-       rmap_item->next = tree_rmap_item->next;
-       rmap_item->prev = tree_rmap_item;
-
-       if (tree_rmap_item->next)
-               tree_rmap_item->next->prev = rmap_item;
-
-       tree_rmap_item->next = rmap_item;
+       rmap_item->head = stable_node;
        rmap_item->address |= STABLE_FLAG;
+       hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
+
+       if (rmap_item->hlist.next)
+               ksm_pages_sharing++;
+       else
+               ksm_pages_shared++;
 }
 
 /*
- * cmp_and_merge_page - take a page computes its hash value and check if there
- * is similar hash value to different page,
- * in case we find that there is similar hash to different page we call to
- * try_to_merge_two_pages().
+ * cmp_and_merge_page - first see if page can be merged into the stable tree;
+ * if not, compare checksum to previous and if it's the same, see if page can
+ * be inserted into the unstable tree, or merged with a page already there and
+ * both transferred to the stable tree.
  *
  * @page: the page that we are searching identical page to.
  * @rmap_item: the reverse mapping into the virtual address of this page
  */
 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
 {
-       struct page *page2[1];
        struct rmap_item *tree_rmap_item;
+       struct page *tree_page = NULL;
+       struct stable_node *stable_node;
+       struct page *kpage;
        unsigned int checksum;
        int err;
 
-       if (in_stable_tree(rmap_item))
-               remove_rmap_item_from_tree(rmap_item);
+       remove_rmap_item_from_tree(rmap_item);
 
        /* We first start with searching the page inside the stable tree */
-       tree_rmap_item = stable_tree_search(page, page2, rmap_item);
-       if (tree_rmap_item) {
-               if (page == page2[0]) {                 /* forked */
-                       ksm_pages_shared++;
-                       err = 0;
-               } else
-                       err = try_to_merge_with_ksm_page(rmap_item->mm,
-                                                        rmap_item->address,
-                                                        page, page2[0]);
-               put_page(page2[0]);
-
+       kpage = stable_tree_search(page);
+       if (kpage) {
+               err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
                if (!err) {
                        /*
                         * The page was successfully merged:
                         * add its rmap_item to the stable tree.
                         */
-                       stable_tree_append(rmap_item, tree_rmap_item);
+                       lock_page(kpage);
+                       stable_tree_append(rmap_item, page_stable_node(kpage));
+                       unlock_page(kpage);
                }
+               put_page(kpage);
                return;
        }
 
        /*
-        * A ksm page might have got here by fork, but its other
-        * references have already been removed from the stable tree.
-        */
-       if (PageKsm(page))
-               break_cow(rmap_item->mm, rmap_item->address);
-
-       /*
-        * In case the hash value of the page was changed from the last time we
-        * have calculated it, this page to be changed frequely, therefore we
-        * don't want to insert it to the unstable tree, and we don't want to
-        * waste our time to search if there is something identical to it there.
+        * If the hash value of the page has changed from the last time
+        * we calculated it, this page is changing frequently: therefore we
+        * don't want to insert it in the unstable tree, and we don't want
+        * to waste our time searching for something identical to it there.
         */
        checksum = calc_checksum(page);
        if (rmap_item->oldchecksum != checksum) {
@@ -1081,58 +1188,56 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
                return;
        }
 
-       tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item);
+       tree_rmap_item =
+               unstable_tree_search_insert(rmap_item, page, &tree_page);
        if (tree_rmap_item) {
-               err = try_to_merge_two_pages(rmap_item->mm,
-                                            rmap_item->address, page,
-                                            tree_rmap_item->mm,
-                                            tree_rmap_item->address, page2[0]);
+               kpage = try_to_merge_two_pages(rmap_item, page,
+                                               tree_rmap_item, tree_page);
+               put_page(tree_page);
                /*
                 * As soon as we merge this page, we want to remove the
                 * rmap_item of the page we have merged with from the unstable
                 * tree, and insert it instead as new node in the stable tree.
                 */
-               if (!err) {
-                       rb_erase(&tree_rmap_item->node, &root_unstable_tree);
-                       tree_rmap_item->address &= ~NODE_FLAG;
+               if (kpage) {
+                       remove_rmap_item_from_tree(tree_rmap_item);
+
+                       lock_page(kpage);
+                       stable_node = stable_tree_insert(kpage);
+                       if (stable_node) {
+                               stable_tree_append(tree_rmap_item, stable_node);
+                               stable_tree_append(rmap_item, stable_node);
+                       }
+                       unlock_page(kpage);
+
                        /*
                         * If we fail to insert the page into the stable tree,
                         * we will have 2 virtual addresses that are pointing
                         * to a ksm page left outside the stable tree,
                         * in which case we need to break_cow on both.
                         */
-                       if (stable_tree_insert(page2[0], tree_rmap_item))
-                               stable_tree_append(rmap_item, tree_rmap_item);
-                       else {
-                               break_cow(tree_rmap_item->mm,
-                                               tree_rmap_item->address);
-                               break_cow(rmap_item->mm, rmap_item->address);
-                               ksm_pages_shared -= 2;
+                       if (!stable_node) {
+                               break_cow(tree_rmap_item);
+                               break_cow(rmap_item);
                        }
                }
-
-               put_page(page2[0]);
        }
 }
 
 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
-                                           struct list_head *cur,
+                                           struct rmap_item **rmap_list,
                                            unsigned long addr)
 {
        struct rmap_item *rmap_item;
 
-       while (cur != &mm_slot->rmap_list) {
-               rmap_item = list_entry(cur, struct rmap_item, link);
-               if ((rmap_item->address & PAGE_MASK) == addr) {
-                       if (!in_stable_tree(rmap_item))
-                               remove_rmap_item_from_tree(rmap_item);
+       while (*rmap_list) {
+               rmap_item = *rmap_list;
+               if ((rmap_item->address & PAGE_MASK) == addr)
                        return rmap_item;
-               }
                if (rmap_item->address > addr)
                        break;
-               cur = cur->next;
+               *rmap_list = rmap_item->rmap_list;
                remove_rmap_item_from_tree(rmap_item);
-               list_del(&rmap_item->link);
                free_rmap_item(rmap_item);
        }
 
@@ -1141,7 +1246,8 @@ static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
                /* It has already been zeroed */
                rmap_item->mm = mm_slot->mm;
                rmap_item->address = addr;
-               list_add_tail(&rmap_item->link, cur);
+               rmap_item->rmap_list = *rmap_list;
+               *rmap_list = rmap_item;
        }
        return rmap_item;
 }
@@ -1166,13 +1272,17 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
                spin_unlock(&ksm_mmlist_lock);
 next_mm:
                ksm_scan.address = 0;
-               ksm_scan.rmap_item = list_entry(&slot->rmap_list,
-                                               struct rmap_item, link);
+               ksm_scan.rmap_list = &slot->rmap_list;
        }
 
        mm = slot->mm;
        down_read(&mm->mmap_sem);
-       for (vma = find_vma(mm, ksm_scan.address); vma; vma = vma->vm_next) {
+       if (ksm_test_exit(mm))
+               vma = NULL;
+       else
+               vma = find_vma(mm, ksm_scan.address);
+
+       for (; vma; vma = vma->vm_next) {
                if (!(vma->vm_flags & VM_MERGEABLE))
                        continue;
                if (ksm_scan.address < vma->vm_start)
@@ -1181,15 +1291,17 @@ next_mm:
                        ksm_scan.address = vma->vm_end;
 
                while (ksm_scan.address < vma->vm_end) {
+                       if (ksm_test_exit(mm))
+                               break;
                        *page = follow_page(vma, ksm_scan.address, FOLL_GET);
                        if (*page && PageAnon(*page)) {
                                flush_anon_page(vma, *page, ksm_scan.address);
                                flush_dcache_page(*page);
                                rmap_item = get_next_rmap_item(slot,
-                                       ksm_scan.rmap_item->link.next,
-                                       ksm_scan.address);
+                                       ksm_scan.rmap_list, ksm_scan.address);
                                if (rmap_item) {
-                                       ksm_scan.rmap_item = rmap_item;
+                                       ksm_scan.rmap_list =
+                                                       &rmap_item->rmap_list;
                                        ksm_scan.address += PAGE_SIZE;
                                } else
                                        put_page(*page);
@@ -1203,40 +1315,47 @@ next_mm:
                }
        }
 
-       if (!ksm_scan.address) {
-               /*
-                * We've completed a full scan of all vmas, holding mmap_sem
-                * throughout, and found no VM_MERGEABLE: so do the same as
-                * __ksm_exit does to remove this mm from all our lists now.
-                */
-               remove_mm_from_lists(mm);
-               up_read(&mm->mmap_sem);
-               slot = ksm_scan.mm_slot;
-               if (slot != &ksm_mm_head)
-                       goto next_mm;
-               return NULL;
+       if (ksm_test_exit(mm)) {
+               ksm_scan.address = 0;
+               ksm_scan.rmap_list = &slot->rmap_list;
        }
-
        /*
         * Nuke all the rmap_items that are above this current rmap:
         * because there were no VM_MERGEABLE vmas with such addresses.
         */
-       remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
-       up_read(&mm->mmap_sem);
+       remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
 
        spin_lock(&ksm_mmlist_lock);
-       slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
-       ksm_scan.mm_slot = slot;
-       spin_unlock(&ksm_mmlist_lock);
+       ksm_scan.mm_slot = list_entry(slot->mm_list.next,
+                                               struct mm_slot, mm_list);
+       if (ksm_scan.address == 0) {
+               /*
+                * We've completed a full scan of all vmas, holding mmap_sem
+                * throughout, and found no VM_MERGEABLE: so do the same as
+                * __ksm_exit does to remove this mm from all our lists now.
+                * This applies either when cleaning up after __ksm_exit
+                * (but beware: we can reach here even before __ksm_exit),
+                * or when all VM_MERGEABLE areas have been unmapped (and
+                * mmap_sem then protects against race with MADV_MERGEABLE).
+                */
+               hlist_del(&slot->link);
+               list_del(&slot->mm_list);
+               spin_unlock(&ksm_mmlist_lock);
+
+               free_mm_slot(slot);
+               clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+               up_read(&mm->mmap_sem);
+               mmdrop(mm);
+       } else {
+               spin_unlock(&ksm_mmlist_lock);
+               up_read(&mm->mmap_sem);
+       }
 
        /* Repeat until we've completed scanning the whole list */
+       slot = ksm_scan.mm_slot;
        if (slot != &ksm_mm_head)
                goto next_mm;
 
-       /*
-        * Bump seqnr here rather than at top, so that __ksm_exit
-        * can skip rb_erase on unstable tree until we run again.
-        */
        ksm_scan.seqnr++;
        return NULL;
 }
@@ -1261,21 +1380,27 @@ static void ksm_do_scan(unsigned int scan_npages)
        }
 }
 
+static int ksmd_should_run(void)
+{
+       return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
+}
+
 static int ksm_scan_thread(void *nothing)
 {
        set_user_nice(current, 5);
 
        while (!kthread_should_stop()) {
-               if (ksm_run & KSM_RUN_MERGE) {
-                       mutex_lock(&ksm_thread_mutex);
+               mutex_lock(&ksm_thread_mutex);
+               if (ksmd_should_run())
                        ksm_do_scan(ksm_thread_pages_to_scan);
-                       mutex_unlock(&ksm_thread_mutex);
+               mutex_unlock(&ksm_thread_mutex);
+
+               if (ksmd_should_run()) {
                        schedule_timeout_interruptible(
                                msecs_to_jiffies(ksm_thread_sleep_millisecs));
                } else {
                        wait_event_interruptible(ksm_thread_wait,
-                                       (ksm_run & KSM_RUN_MERGE) ||
-                                       kthread_should_stop());
+                               ksmd_should_run() || kthread_should_stop());
                }
        }
        return 0;
@@ -1285,6 +1410,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
                unsigned long end, int advice, unsigned long *vm_flags)
 {
        struct mm_struct *mm = vma->vm_mm;
+       int err;
 
        switch (advice) {
        case MADV_MERGEABLE:
@@ -1294,12 +1420,14 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
                if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
                                 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
                                 VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
-                                VM_MIXEDMAP  | VM_SAO))
+                                VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
                        return 0;               /* just ignore the advice */
 
-               if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
-                       if (__ksm_enter(mm) < 0)
-                               return -EAGAIN;
+               if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
+                       err = __ksm_enter(mm);
+                       if (err)
+                               return err;
+               }
 
                *vm_flags |= VM_MERGEABLE;
                break;
@@ -1308,8 +1436,11 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
                if (!(*vm_flags & VM_MERGEABLE))
                        return 0;               /* just ignore the advice */
 
-               if (vma->anon_vma)
-                       unmerge_ksm_pages(vma, start, end);
+               if (vma->anon_vma) {
+                       err = unmerge_ksm_pages(vma, start, end);
+                       if (err)
+                               return err;
+               }
 
                *vm_flags &= ~VM_MERGEABLE;
                break;
@@ -1320,10 +1451,16 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 
 int __ksm_enter(struct mm_struct *mm)
 {
-       struct mm_slot *mm_slot = alloc_mm_slot();
+       struct mm_slot *mm_slot;
+       int needs_wakeup;
+
+       mm_slot = alloc_mm_slot();
        if (!mm_slot)
                return -ENOMEM;
 
+       /* Check ksm_run too?  Would need tighter locking */
+       needs_wakeup = list_empty(&ksm_mm_head.mm_list);
+
        spin_lock(&ksm_mmlist_lock);
        insert_to_mm_slots_hash(mm, mm_slot);
        /*
@@ -1335,21 +1472,306 @@ int __ksm_enter(struct mm_struct *mm)
        spin_unlock(&ksm_mmlist_lock);
 
        set_bit(MMF_VM_MERGEABLE, &mm->flags);
+       atomic_inc(&mm->mm_count);
+
+       if (needs_wakeup)
+               wake_up_interruptible(&ksm_thread_wait);
+
        return 0;
 }
 
 void __ksm_exit(struct mm_struct *mm)
 {
+       struct mm_slot *mm_slot;
+       int easy_to_free = 0;
+
        /*
-        * This process is exiting: doesn't hold and doesn't need mmap_sem;
-        * but we do need to exclude ksmd and other exiters while we modify
-        * the various lists and trees.
+        * This process is exiting: if it's straightforward (as is the
+        * case when ksmd was never running), free mm_slot immediately.
+        * But if it's at the cursor or has rmap_items linked to it, use
+        * mmap_sem to synchronize with any break_cows before pagetables
+        * are freed, and leave the mm_slot on the list for ksmd to free.
+        * Beware: ksm may already have noticed it exiting and freed the slot.
         */
-       mutex_lock(&ksm_thread_mutex);
-       remove_mm_from_lists(mm);
-       mutex_unlock(&ksm_thread_mutex);
+
+       spin_lock(&ksm_mmlist_lock);
+       mm_slot = get_mm_slot(mm);
+       if (mm_slot && ksm_scan.mm_slot != mm_slot) {
+               if (!mm_slot->rmap_list) {
+                       hlist_del(&mm_slot->link);
+                       list_del(&mm_slot->mm_list);
+                       easy_to_free = 1;
+               } else {
+                       list_move(&mm_slot->mm_list,
+                                 &ksm_scan.mm_slot->mm_list);
+               }
+       }
+       spin_unlock(&ksm_mmlist_lock);
+
+       if (easy_to_free) {
+               free_mm_slot(mm_slot);
+               clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+               mmdrop(mm);
+       } else if (mm_slot) {
+               down_write(&mm->mmap_sem);
+               up_write(&mm->mmap_sem);
+       }
 }
 
+struct page *ksm_does_need_to_copy(struct page *page,
+                       struct vm_area_struct *vma, unsigned long address)
+{
+       struct page *new_page;
+
+       unlock_page(page);      /* any racers will COW it, not modify it */
+
+       new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
+       if (new_page) {
+               copy_user_highpage(new_page, page, address, vma);
+
+               SetPageDirty(new_page);
+               __SetPageUptodate(new_page);
+               SetPageSwapBacked(new_page);
+               __set_page_locked(new_page);
+
+               if (page_evictable(new_page, vma))
+                       lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
+               else
+                       add_page_to_unevictable_list(new_page);
+       }
+
+       page_cache_release(page);
+       return new_page;
+}
+
+int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
+                       unsigned long *vm_flags)
+{
+       struct stable_node *stable_node;
+       struct rmap_item *rmap_item;
+       struct hlist_node *hlist;
+       unsigned int mapcount = page_mapcount(page);
+       int referenced = 0;
+       int search_new_forks = 0;
+
+       VM_BUG_ON(!PageKsm(page));
+       VM_BUG_ON(!PageLocked(page));
+
+       stable_node = page_stable_node(page);
+       if (!stable_node)
+               return 0;
+again:
+       hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
+               struct anon_vma *anon_vma = rmap_item->anon_vma;
+               struct anon_vma_chain *vmac;
+               struct vm_area_struct *vma;
+
+               spin_lock(&anon_vma->lock);
+               list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
+                       vma = vmac->vma;
+                       if (rmap_item->address < vma->vm_start ||
+                           rmap_item->address >= vma->vm_end)
+                               continue;
+                       /*
+                        * Initially we examine only the vma which covers this
+                        * rmap_item; but later, if there is still work to do,
+                        * we examine covering vmas in other mms: in case they
+                        * were forked from the original since ksmd passed.
+                        */
+                       if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
+                               continue;
+
+                       if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
+                               continue;
+
+                       referenced += page_referenced_one(page, vma,
+                               rmap_item->address, &mapcount, vm_flags);
+                       if (!search_new_forks || !mapcount)
+                               break;
+               }
+               spin_unlock(&anon_vma->lock);
+               if (!mapcount)
+                       goto out;
+       }
+       if (!search_new_forks++)
+               goto again;
+out:
+       return referenced;
+}
+
+int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
+{
+       struct stable_node *stable_node;
+       struct hlist_node *hlist;
+       struct rmap_item *rmap_item;
+       int ret = SWAP_AGAIN;
+       int search_new_forks = 0;
+
+       VM_BUG_ON(!PageKsm(page));
+       VM_BUG_ON(!PageLocked(page));
+
+       stable_node = page_stable_node(page);
+       if (!stable_node)
+               return SWAP_FAIL;
+again:
+       hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
+               struct anon_vma *anon_vma = rmap_item->anon_vma;
+               struct anon_vma_chain *vmac;
+               struct vm_area_struct *vma;
+
+               spin_lock(&anon_vma->lock);
+               list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
+                       vma = vmac->vma;
+                       if (rmap_item->address < vma->vm_start ||
+                           rmap_item->address >= vma->vm_end)
+                               continue;
+                       /*
+                        * Initially we examine only the vma which covers this
+                        * rmap_item; but later, if there is still work to do,
+                        * we examine covering vmas in other mms: in case they
+                        * were forked from the original since ksmd passed.
+                        */
+                       if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
+                               continue;
+
+                       ret = try_to_unmap_one(page, vma,
+                                       rmap_item->address, flags);
+                       if (ret != SWAP_AGAIN || !page_mapped(page)) {
+                               spin_unlock(&anon_vma->lock);
+                               goto out;
+                       }
+               }
+               spin_unlock(&anon_vma->lock);
+       }
+       if (!search_new_forks++)
+               goto again;
+out:
+       return ret;
+}
+
+#ifdef CONFIG_MIGRATION
+int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
+                 struct vm_area_struct *, unsigned long, void *), void *arg)
+{
+       struct stable_node *stable_node;
+       struct hlist_node *hlist;
+       struct rmap_item *rmap_item;
+       int ret = SWAP_AGAIN;
+       int search_new_forks = 0;
+
+       VM_BUG_ON(!PageKsm(page));
+       VM_BUG_ON(!PageLocked(page));
+
+       stable_node = page_stable_node(page);
+       if (!stable_node)
+               return ret;
+again:
+       hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
+               struct anon_vma *anon_vma = rmap_item->anon_vma;
+               struct anon_vma_chain *vmac;
+               struct vm_area_struct *vma;
+
+               spin_lock(&anon_vma->lock);
+               list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
+                       vma = vmac->vma;
+                       if (rmap_item->address < vma->vm_start ||
+                           rmap_item->address >= vma->vm_end)
+                               continue;
+                       /*
+                        * Initially we examine only the vma which covers this
+                        * rmap_item; but later, if there is still work to do,
+                        * we examine covering vmas in other mms: in case they
+                        * were forked from the original since ksmd passed.
+                        */
+                       if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
+                               continue;
+
+                       ret = rmap_one(page, vma, rmap_item->address, arg);
+                       if (ret != SWAP_AGAIN) {
+                               spin_unlock(&anon_vma->lock);
+                               goto out;
+                       }
+               }
+               spin_unlock(&anon_vma->lock);
+       }
+       if (!search_new_forks++)
+               goto again;
+out:
+       return ret;
+}
+
+void ksm_migrate_page(struct page *newpage, struct page *oldpage)
+{
+       struct stable_node *stable_node;
+
+       VM_BUG_ON(!PageLocked(oldpage));
+       VM_BUG_ON(!PageLocked(newpage));
+       VM_BUG_ON(newpage->mapping != oldpage->mapping);
+
+       stable_node = page_stable_node(newpage);
+       if (stable_node) {
+               VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
+               stable_node->kpfn = page_to_pfn(newpage);
+       }
+}
+#endif /* CONFIG_MIGRATION */
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
+                                                unsigned long end_pfn)
+{
+       struct rb_node *node;
+
+       for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
+               struct stable_node *stable_node;
+
+               stable_node = rb_entry(node, struct stable_node, node);
+               if (stable_node->kpfn >= start_pfn &&
+                   stable_node->kpfn < end_pfn)
+                       return stable_node;
+       }
+       return NULL;
+}
+
+static int ksm_memory_callback(struct notifier_block *self,
+                              unsigned long action, void *arg)
+{
+       struct memory_notify *mn = arg;
+       struct stable_node *stable_node;
+
+       switch (action) {
+       case MEM_GOING_OFFLINE:
+               /*
+                * Keep it very simple for now: just lock out ksmd and
+                * MADV_UNMERGEABLE while any memory is going offline.
+                */
+               mutex_lock(&ksm_thread_mutex);
+               break;
+
+       case MEM_OFFLINE:
+               /*
+                * Most of the work is done by page migration; but there might
+                * be a few stable_nodes left over, still pointing to struct
+                * pages which have been offlined: prune those from the tree.
+                */
+               while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
+                                       mn->start_pfn + mn->nr_pages)) != NULL)
+                       remove_node_from_stable_tree(stable_node);
+               /* fallthrough */
+
+       case MEM_CANCEL_OFFLINE:
+               mutex_unlock(&ksm_thread_mutex);
+               break;
+       }
+       return NOTIFY_OK;
+}
+#endif /* CONFIG_MEMORY_HOTREMOVE */
+
+#ifdef CONFIG_SYSFS
+/*
+ * This all compiles without CONFIG_SYSFS, but is a waste of space.
+ */
+
 #define KSM_ATTR_RO(_name) \
        static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
 #define KSM_ATTR(_name) \
@@ -1423,15 +1845,22 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
        /*
         * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
         * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
-        * breaking COW to free the kernel_pages_allocated (but leaves
-        * mm_slots on the list for when ksmd may be set running again).
+        * breaking COW to free the pages_shared (but leaves mm_slots
+        * on the list for when ksmd may be set running again).
         */
 
        mutex_lock(&ksm_thread_mutex);
        if (ksm_run != flags) {
                ksm_run = flags;
-               if (flags & KSM_RUN_UNMERGE)
-                       unmerge_and_remove_all_rmap_items();
+               if (flags & KSM_RUN_UNMERGE) {
+                       current->flags |= PF_OOM_ORIGIN;
+                       err = unmerge_and_remove_all_rmap_items();
+                       current->flags &= ~PF_OOM_ORIGIN;
+                       if (err) {
+                               ksm_run = KSM_RUN_STOP;
+                               count = err;
+                       }
+               }
        }
        mutex_unlock(&ksm_thread_mutex);
 
@@ -1445,49 +1874,57 @@ KSM_ATTR(run);
 static ssize_t pages_shared_show(struct kobject *kobj,
                                 struct kobj_attribute *attr, char *buf)
 {
-       return sprintf(buf, "%lu\n",
-                       ksm_pages_shared - ksm_kernel_pages_allocated);
+       return sprintf(buf, "%lu\n", ksm_pages_shared);
 }
 KSM_ATTR_RO(pages_shared);
 
-static ssize_t kernel_pages_allocated_show(struct kobject *kobj,
-                                          struct kobj_attribute *attr,
-                                          char *buf)
+static ssize_t pages_sharing_show(struct kobject *kobj,
+                                 struct kobj_attribute *attr, char *buf)
 {
-       return sprintf(buf, "%lu\n", ksm_kernel_pages_allocated);
+       return sprintf(buf, "%lu\n", ksm_pages_sharing);
 }
-KSM_ATTR_RO(kernel_pages_allocated);
+KSM_ATTR_RO(pages_sharing);
 
-static ssize_t max_kernel_pages_store(struct kobject *kobj,
-                                     struct kobj_attribute *attr,
-                                     const char *buf, size_t count)
+static ssize_t pages_unshared_show(struct kobject *kobj,
+                                  struct kobj_attribute *attr, char *buf)
 {
-       int err;
-       unsigned long nr_pages;
-
-       err = strict_strtoul(buf, 10, &nr_pages);
-       if (err)
-               return -EINVAL;
+       return sprintf(buf, "%lu\n", ksm_pages_unshared);
+}
+KSM_ATTR_RO(pages_unshared);
 
-       ksm_max_kernel_pages = nr_pages;
+static ssize_t pages_volatile_show(struct kobject *kobj,
+                                  struct kobj_attribute *attr, char *buf)
+{
+       long ksm_pages_volatile;
 
-       return count;
+       ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
+                               - ksm_pages_sharing - ksm_pages_unshared;
+       /*
+        * It was not worth any locking to calculate that statistic,
+        * but it might therefore sometimes be negative: conceal that.
+        */
+       if (ksm_pages_volatile < 0)
+               ksm_pages_volatile = 0;
+       return sprintf(buf, "%ld\n", ksm_pages_volatile);
 }
+KSM_ATTR_RO(pages_volatile);
 
-static ssize_t max_kernel_pages_show(struct kobject *kobj,
-                                    struct kobj_attribute *attr, char *buf)
+static ssize_t full_scans_show(struct kobject *kobj,
+                              struct kobj_attribute *attr, char *buf)
 {
-       return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
+       return sprintf(buf, "%lu\n", ksm_scan.seqnr);
 }
-KSM_ATTR(max_kernel_pages);
+KSM_ATTR_RO(full_scans);
 
 static struct attribute *ksm_attrs[] = {
        &sleep_millisecs_attr.attr,
        &pages_to_scan_attr.attr,
        &run_attr.attr,
        &pages_shared_attr.attr,
-       &kernel_pages_allocated_attr.attr,
-       &max_kernel_pages_attr.attr,
+       &pages_sharing_attr.attr,
+       &pages_unshared_attr.attr,
+       &pages_volatile_attr.attr,
+       &full_scans_attr.attr,
        NULL,
 };
 
@@ -1495,6 +1932,7 @@ static struct attribute_group ksm_attr_group = {
        .attrs = ksm_attrs,
        .name = "ksm",
 };
+#endif /* CONFIG_SYSFS */
 
 static int __init ksm_init(void)
 {
@@ -1516,16 +1954,27 @@ static int __init ksm_init(void)
                goto out_free2;
        }
 
+#ifdef CONFIG_SYSFS
        err = sysfs_create_group(mm_kobj, &ksm_attr_group);
        if (err) {
                printk(KERN_ERR "ksm: register sysfs failed\n");
-               goto out_free3;
+               kthread_stop(ksm_thread);
+               goto out_free2;
        }
+#else
+       ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
 
+#endif /* CONFIG_SYSFS */
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+       /*
+        * Choose a high priority since the callback takes ksm_thread_mutex:
+        * later callbacks could only be taking locks which nest within that.
+        */
+       hotplug_memory_notifier(ksm_memory_callback, 100);
+#endif
        return 0;
 
-out_free3:
-       kthread_stop(ksm_thread);
 out_free2:
        mm_slots_hash_free();
 out_free1: