SHM_LOCKED pages are unevictable
Lee Schermerhorn [Sun, 19 Oct 2008 03:26:43 +0000 (20:26 -0700)]
Shmem segments locked into memory via shmctl(SHM_LOCKED) should not be
kept on the normal LRU, since scanning them is a waste of time and might
throw off kswapd's balancing algorithms.  Place them on the unevictable
LRU list instead.

Use the AS_UNEVICTABLE flag to mark address_space of SHM_LOCKed shared
memory regions as unevictable.  Then these pages will be culled off the
normal LRU lists during vmscan.

Add new wrapper function to clear the mapping's unevictable state when/if
shared memory segment is munlocked.

Add 'scan_mapping_unevictable_page()' to mm/vmscan.c to scan all pages in
the shmem segment's mapping [struct address_space] for evictability now
that they're no longer locked.  If so, move them to the appropriate zone
lru list.

Changes depend on [CONFIG_]UNEVICTABLE_LRU.

[kosaki.motohiro@jp.fujitsu.com: revert shm change]
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h
include/linux/pagemap.h
include/linux/swap.h
ipc/shm.c
mm/shmem.c
mm/vmscan.c

index c61ba10..4023629 100644 (file)
@@ -700,10 +700,10 @@ static inline int page_mapped(struct page *page)
 extern void show_free_areas(void);
 
 #ifdef CONFIG_SHMEM
-int shmem_lock(struct file *file, int lock, struct user_struct *user);
+extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
 #else
 static inline int shmem_lock(struct file *file, int lock,
-                            struct user_struct *user)
+                           struct user_struct *user)
 {
        return 0;
 }
index 09164d2..4b6c4d8 100644 (file)
@@ -40,14 +40,20 @@ static inline void mapping_set_unevictable(struct address_space *mapping)
        set_bit(AS_UNEVICTABLE, &mapping->flags);
 }
 
+static inline void mapping_clear_unevictable(struct address_space *mapping)
+{
+       clear_bit(AS_UNEVICTABLE, &mapping->flags);
+}
+
 static inline int mapping_unevictable(struct address_space *mapping)
 {
-       if (mapping && (mapping->flags & AS_UNEVICTABLE))
-               return 1;
-       return 0;
+       if (likely(mapping))
+               return test_bit(AS_UNEVICTABLE, &mapping->flags);
+       return !!mapping;
 }
 #else
 static inline void mapping_set_unevictable(struct address_space *mapping) { }
+static inline void mapping_clear_unevictable(struct address_space *mapping) { }
 static inline int mapping_unevictable(struct address_space *mapping)
 {
        return 0;
index a211304..7edb4cb 100644 (file)
@@ -232,12 +232,16 @@ static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
 
 #ifdef CONFIG_UNEVICTABLE_LRU
 extern int page_evictable(struct page *page, struct vm_area_struct *vma);
+extern void scan_mapping_unevictable_pages(struct address_space *);
 #else
 static inline int page_evictable(struct page *page,
                                                struct vm_area_struct *vma)
 {
        return 1;
 }
+static inline void scan_mapping_unevictable_pages(struct address_space *mapping)
+{
+}
 #endif
 
 extern int kswapd_run(int nid);
index e77ec69..0add3fa 100644 (file)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -737,6 +737,10 @@ asmlinkage long sys_shmctl(int shmid, int cmd, struct shmid_ds __user *buf)
        case SHM_LOCK:
        case SHM_UNLOCK:
        {
+               struct file *uninitialized_var(shm_file);
+
+               lru_add_drain_all();  /* drain pagevecs to lru lists */
+
                shp = shm_lock_check(ns, shmid);
                if (IS_ERR(shp)) {
                        err = PTR_ERR(shp);
index fc2ccf7..d38d7e6 100644 (file)
@@ -1477,12 +1477,16 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
                if (!user_shm_lock(inode->i_size, user))
                        goto out_nomem;
                info->flags |= VM_LOCKED;
+               mapping_set_unevictable(file->f_mapping);
        }
        if (!lock && (info->flags & VM_LOCKED) && user) {
                user_shm_unlock(inode->i_size, user);
                info->flags &= ~VM_LOCKED;
+               mapping_clear_unevictable(file->f_mapping);
+               scan_mapping_unevictable_pages(file->f_mapping);
        }
        retval = 0;
+
 out_nomem:
        spin_unlock(&info->lock);
        return retval;
index 9babfbc..dfb342e 100644 (file)
@@ -2346,4 +2346,93 @@ int page_evictable(struct page *page, struct vm_area_struct *vma)
 
        return 1;
 }
+
+/**
+ * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
+ * @page: page to check evictability and move to appropriate lru list
+ * @zone: zone page is in
+ *
+ * Checks a page for evictability and moves the page to the appropriate
+ * zone lru list.
+ *
+ * Restrictions: zone->lru_lock must be held, page must be on LRU and must
+ * have PageUnevictable set.
+ */
+static void check_move_unevictable_page(struct page *page, struct zone *zone)
+{
+       VM_BUG_ON(PageActive(page));
+
+retry:
+       ClearPageUnevictable(page);
+       if (page_evictable(page, NULL)) {
+               enum lru_list l = LRU_INACTIVE_ANON + page_is_file_cache(page);
+               __dec_zone_state(zone, NR_UNEVICTABLE);
+               list_move(&page->lru, &zone->lru[l].list);
+               __inc_zone_state(zone, NR_INACTIVE_ANON + l);
+               __count_vm_event(UNEVICTABLE_PGRESCUED);
+       } else {
+               /*
+                * rotate unevictable list
+                */
+               SetPageUnevictable(page);
+               list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
+               if (page_evictable(page, NULL))
+                       goto retry;
+       }
+}
+
+/**
+ * scan_mapping_unevictable_pages - scan an address space for evictable pages
+ * @mapping: struct address_space to scan for evictable pages
+ *
+ * Scan all pages in mapping.  Check unevictable pages for
+ * evictability and move them to the appropriate zone lru list.
+ */
+void scan_mapping_unevictable_pages(struct address_space *mapping)
+{
+       pgoff_t next = 0;
+       pgoff_t end   = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
+                        PAGE_CACHE_SHIFT;
+       struct zone *zone;
+       struct pagevec pvec;
+
+       if (mapping->nrpages == 0)
+               return;
+
+       pagevec_init(&pvec, 0);
+       while (next < end &&
+               pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
+               int i;
+               int pg_scanned = 0;
+
+               zone = NULL;
+
+               for (i = 0; i < pagevec_count(&pvec); i++) {
+                       struct page *page = pvec.pages[i];
+                       pgoff_t page_index = page->index;
+                       struct zone *pagezone = page_zone(page);
+
+                       pg_scanned++;
+                       if (page_index > next)
+                               next = page_index;
+                       next++;
+
+                       if (pagezone != zone) {
+                               if (zone)
+                                       spin_unlock_irq(&zone->lru_lock);
+                               zone = pagezone;
+                               spin_lock_irq(&zone->lru_lock);
+                       }
+
+                       if (PageLRU(page) && PageUnevictable(page))
+                               check_move_unevictable_page(page, zone);
+               }
+               if (zone)
+                       spin_unlock_irq(&zone->lru_lock);
+               pagevec_release(&pvec);
+
+               count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
+       }
+
+}
 #endif