ksm: cleanup some function arguments
Hugh Dickins [Tue, 15 Dec 2009 01:59:18 +0000 (17:59 -0800)]
Cleanup: make argument names more consistent from cmp_and_merge_page()
down to replace_page(), so that it's easier to follow the rmap_item's page
and the matching tree_page and the merged kpage through that code.

In some places, e.g.  break_cow(), pass rmap_item instead of separate mm
and address.

cmp_and_merge_page() initialize tree_page to NULL, to avoid a "may be used
uninitialized" warning seen in one config by Anil SB.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/ksm.c

index fdd7d5f..54fb3fe 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -356,8 +356,10 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
        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;
 
        down_read(&mm->mmap_sem);
@@ -665,15 +667,15 @@ 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;
@@ -684,7 +686,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
        unsigned long addr;
        int err = -EFAULT;
 
-       addr = page_address_in_vma(oldpage, vma);
+       addr = page_address_in_vma(page, vma);
        if (addr == -EFAULT)
                goto out;
 
@@ -706,15 +708,15 @@ 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_ksm_rmap(kpage);
 
        flush_cache_page(vma, addr, pte_pfn(*ptep));
        ptep_clear_flush(vma, addr, ptep);
-       set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, vma->vm_page_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;
@@ -724,26 +726,22 @@ 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 (or newly allocated page which page_add_ksm_rmap
+ *         will make PageKsm) that we want to map instead of page
  *
  * 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 (!(vma->vm_flags & VM_MERGEABLE))
                goto out;
-       if (!PageAnon(oldpage))
+       if (!PageAnon(page))
                goto out;
 
        /*
@@ -753,7 +751,7 @@ 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))
+       if (!trylock_page(page))
                goto out;
        /*
         * If this anonymous page is mapped only here, its pte may need
@@ -761,11 +759,11 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
         * 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) == 0 &&
-           pages_identical(oldpage, newpage))
-               err = replace_page(vma, oldpage, newpage, orig_pte);
+       if (write_protect_page(vma, page, &orig_pte) == 0 &&
+           pages_identical(page, kpage))
+               err = replace_page(vma, page, kpage, orig_pte);
 
-       unlock_page(oldpage);
+       unlock_page(page);
 out:
        return err;
 }
@@ -773,26 +771,26 @@ out:
 /*
  * 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.
+ *
+ * This function returns 0 if the pages were merged, -EFAULT otherwise.
  */
-static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
-                                     unsigned long addr1,
-                                     struct page *page1,
-                                     struct page *kpage)
+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;
        int err = -EFAULT;
 
-       down_read(&mm1->mmap_sem);
-       if (ksm_test_exit(mm1))
+       down_read(&mm->mmap_sem);
+       if (ksm_test_exit(mm))
                goto out;
-
-       vma = find_vma(mm1, addr1);
-       if (!vma || vma->vm_start > addr1)
+       vma = find_vma(mm, rmap_item->address);
+       if (!vma || vma->vm_start > rmap_item->address)
                goto out;
 
-       err = try_to_merge_one_page(vma, page1, kpage);
+       err = try_to_merge_one_page(vma, page, kpage);
 out:
-       up_read(&mm1->mmap_sem);
+       up_read(&mm->mmap_sem);
        return err;
 }
 
@@ -800,16 +798,18 @@ out:
  * 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.
+ * This function returns the kpage if we successfully merged two identical
+ * pages into one ksm page, NULL otherwise.
  *
  * 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.
  */
-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 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 mm_struct *mm = rmap_item->mm;
        struct vm_area_struct *vma;
        struct page *kpage;
        int err = -EFAULT;
@@ -820,47 +820,43 @@ static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
         */
        if (ksm_max_kernel_pages &&
            ksm_max_kernel_pages <= ksm_pages_shared)
-               return err;
+               return NULL;
 
        kpage = alloc_page(GFP_HIGHUSER);
        if (!kpage)
-               return err;
-
-       down_read(&mm1->mmap_sem);
-       if (ksm_test_exit(mm1)) {
-               up_read(&mm1->mmap_sem);
-               goto out;
-       }
-       vma = find_vma(mm1, addr1);
-       if (!vma || vma->vm_start > addr1) {
-               up_read(&mm1->mmap_sem);
-               goto out;
-       }
+               return NULL;
 
-       copy_user_highpage(kpage, page1, addr1, vma);
-       err = try_to_merge_one_page(vma, page1, kpage);
-       up_read(&mm1->mmap_sem);
+       down_read(&mm->mmap_sem);
+       if (ksm_test_exit(mm))
+               goto up;
+       vma = find_vma(mm, rmap_item->address);
+       if (!vma || vma->vm_start > rmap_item->address)
+               goto up;
+
+       copy_user_highpage(kpage, page, rmap_item->address, vma);
+       err = try_to_merge_one_page(vma, page, kpage);
+up:
+       up_read(&mm->mmap_sem);
 
        if (!err) {
-               err = try_to_merge_with_ksm_page(mm2, addr2, page2, kpage);
+               err = try_to_merge_with_ksm_page(tree_rmap_item,
+                                                       tree_page, kpage);
                /*
                 * If that fails, we have a ksm page with only one pte
                 * pointing to it: so break it.
                 */
                if (err)
-                       break_cow(mm1, addr1);
+                       break_cow(rmap_item);
        }
-out:
-       put_page(kpage);
-       return err;
+       if (err) {
+               put_page(kpage);
+               kpage = NULL;
+       }
+       return kpage;
 }
 
 /*
- * 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.
@@ -869,21 +865,21 @@ out:
  * NULL otherwise.
  */
 static struct rmap_item *stable_tree_search(struct page *page,
-                                           struct page **page2,
-                                           struct rmap_item *rmap_item)
+                                           struct page **tree_pagep)
 {
        struct rb_node *node = root_stable_tree.rb_node;
 
        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])
+                       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);
@@ -892,15 +888,16 @@ static struct rmap_item *stable_tree_search(struct page *page,
                if (!tree_rmap_item)
                        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 {
+                       *tree_pagep = tree_page;
                        return tree_rmap_item;
                }
        }
@@ -912,13 +909,9 @@ 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.
  */
-static struct rmap_item *stable_tree_insert(struct page *page,
+static struct rmap_item *stable_tree_insert(struct page *kpage,
                                            struct rmap_item *rmap_item)
 {
        struct rb_node **new = &root_stable_tree.rb_node;
@@ -943,7 +936,7 @@ static struct rmap_item *stable_tree_insert(struct page *page,
                if (!tree_rmap_item)
                        return NULL;
 
-               ret = memcmp_pages(page, tree_page);
+               ret = memcmp_pages(kpage, tree_page);
                put_page(tree_page);
 
                parent = *new;
@@ -971,12 +964,8 @@ static struct rmap_item *stable_tree_insert(struct page *page,
 }
 
 /*
- * 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
@@ -988,42 +977,45 @@ 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;
                }
        }
@@ -1068,24 +1060,23 @@ static void stable_tree_append(struct rmap_item *rmap_item,
  */
 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 page *kpage;
        unsigned int checksum;
        int err;
 
        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);
+       tree_rmap_item = stable_tree_search(page, &tree_page);
        if (tree_rmap_item) {
-               if (page == page2[0])                   /* forked */
+               kpage = tree_page;
+               if (page == kpage)                      /* forked */
                        err = 0;
                else
-                       err = try_to_merge_with_ksm_page(rmap_item->mm,
-                                                        rmap_item->address,
-                                                        page, page2[0]);
-               put_page(page2[0]);
-
+                       err = try_to_merge_with_ksm_page(rmap_item,
+                                                        page, kpage);
                if (!err) {
                        /*
                         * The page was successfully merged:
@@ -1093,6 +1084,7 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
                         */
                        stable_tree_append(rmap_item, tree_rmap_item);
                }
+               put_page(kpage);
                return;
        }
 
@@ -1103,7 +1095,7 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
         * when the mem_cgroup had reached its limit: try again now.
         */
        if (PageKsm(page))
-               break_cow(rmap_item->mm, rmap_item->address);
+               break_cow(rmap_item);
 
        /*
         * In case the hash value of the page was changed from the last time we
@@ -1117,18 +1109,18 @@ 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) {
+               if (kpage) {
                        remove_rmap_item_from_tree(tree_rmap_item);
 
                        /*
@@ -1137,16 +1129,14 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
                         * 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))
+                       if (stable_tree_insert(kpage, 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);
+                               break_cow(tree_rmap_item);
+                               break_cow(rmap_item);
                        }
+                       put_page(kpage);
                }
-
-               put_page(page2[0]);
        }
 }
 
@@ -1308,7 +1298,7 @@ static void ksm_do_scan(unsigned int scan_npages)
                        /*
                         * Replace now-unshared ksm page by ordinary page.
                         */
-                       break_cow(rmap_item->mm, rmap_item->address);
+                       break_cow(rmap_item);
                        remove_rmap_item_from_tree(rmap_item);
                        rmap_item->oldchecksum = calc_checksum(page);
                }