SHM_UNLOCK: fix Unevictable pages stranded after swap

commit 245132643e1cfcd145bbc86a716c1818371fcb93 upstream.

Commit cc39c6a9bbde ("mm: account skipped entries to avoid looping in
find_get_pages") correctly fixed an infinite loop; but left a problem
that find_get_pages() on shmem would return 0 (appearing to callers to
mean end of tree) when it meets a run of nr_pages swap entries.

The only uses of find_get_pages() on shmem are via pagevec_lookup(),
called from invalidate_mapping_pages(), and from shmctl SHM_UNLOCK's
scan_mapping_unevictable_pages().  The first is already commented, and
not worth worrying about; but the second can leave pages on the
Unevictable list after an unusual sequence of swapping and locking.

Fix that by using shmem_find_get_pages_and_swap() (then ignoring the
swap) instead of pagevec_lookup().

But I don't want to contaminate vmscan.c with shmem internals, nor
shmem.c with LRU locking.  So move scan_mapping_unevictable_pages() into
shmem.c, renaming it shmem_unlock_mapping(); and rename
check_move_unevictable_page() to check_move_unevictable_pages(), looping
down an array of pages, oftentimes under the same lock.

Leave out the "rotate unevictable list" block: that's a leftover from
when this was used for /proc/sys/vm/scan_unevictable_pages, whose flawed
handling involved looking at pages at tail of LRU.

Was there significance to the sequence first ClearPageUnevictable, then
test page_evictable, then SetPageUnevictable here? I think not, we're
under LRU lock, and have no barriers between those.

Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 9291ac3..6f10c9c 100644 (file)
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -48,6 +48,7 @@ extern struct file *shmem_file_setup(const char *name,
                                        loff_t size, unsigned long flags);
 extern int shmem_zero_setup(struct vm_area_struct *);
 extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
+extern void shmem_unlock_mapping(struct address_space *mapping);
 extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
                                        pgoff_t index, gfp_t gfp_mask);
 extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 1e22e12..67b3fa3 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -272,7 +272,7 @@ static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
 #endif
 
 extern int page_evictable(struct page *page, struct vm_area_struct *vma);
-extern void scan_mapping_unevictable_pages(struct address_space *);
+extern void check_move_unevictable_pages(struct page **, int nr_pages);
 
 extern unsigned long scan_unevictable_pages;
 extern int scan_unevictable_handler(struct ctl_table *, int,

diff --git a/ipc/shm.c b/ipc/shm.c
index 854ab58..b76be5b 100644 (file)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -916,7 +916,7 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
                shp->mlock_user = NULL;
                get_file(shm_file);
                shm_unlock(shp);
-               scan_mapping_unevictable_pages(shm_file->f_mapping);
+               shmem_unlock_mapping(shm_file->f_mapping);
                fput(shm_file);
                goto out;
        }

diff --git a/mm/shmem.c b/mm/shmem.c
index cc6d40b..6c253f7 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -379,7 +379,7 @@ static int shmem_free_swap(struct address_space *mapping,
 /*
  * Pagevec may contain swap entries, so shuffle up pages before releasing.
  */
-static void shmem_pagevec_release(struct pagevec *pvec)
+static void shmem_deswap_pagevec(struct pagevec *pvec)
 {
        int i, j;
 
@@ -389,7 +389,36 @@ static void shmem_pagevec_release(struct pagevec *pvec)
                        pvec->pages[j++] = page;
        }
        pvec->nr = j;
-       pagevec_release(pvec);
+}
+
+/*
+ * SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
+ */
+void shmem_unlock_mapping(struct address_space *mapping)
+{
+       struct pagevec pvec;
+       pgoff_t indices[PAGEVEC_SIZE];
+       pgoff_t index = 0;
+
+       pagevec_init(&pvec, 0);
+       /*
+        * Minor point, but we might as well stop if someone else SHM_LOCKs it.
+        */
+       while (!mapping_unevictable(mapping)) {
+               /*
+                * Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
+                * has finished, if it hits a row of PAGEVEC_SIZE swap entries.
+                */
+               pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
+                                       PAGEVEC_SIZE, pvec.pages, indices);
+               if (!pvec.nr)
+                       break;
+               index = indices[pvec.nr - 1] + 1;
+               shmem_deswap_pagevec(&pvec);
+               check_move_unevictable_pages(pvec.pages, pvec.nr);
+               pagevec_release(&pvec);
+               cond_resched();
+       }
 }
 
 /*
@@ -440,7 +469,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
                        }
                        unlock_page(page);
                }
-               shmem_pagevec_release(&pvec);
+               shmem_deswap_pagevec(&pvec);
+               pagevec_release(&pvec);
                mem_cgroup_uncharge_end();
                cond_resched();
                index++;
@@ -470,7 +500,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
                        continue;
                }
                if (index == start && indices[0] > end) {
-                       shmem_pagevec_release(&pvec);
+                       shmem_deswap_pagevec(&pvec);
+                       pagevec_release(&pvec);
                        break;
                }
                mem_cgroup_uncharge_start();
@@ -494,7 +525,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
                        }
                        unlock_page(page);
                }
-               shmem_pagevec_release(&pvec);
+               shmem_deswap_pagevec(&pvec);
+               pagevec_release(&pvec);
                mem_cgroup_uncharge_end();
                index++;
        }
@@ -2439,6 +2471,10 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
        return 0;
 }
 
+void shmem_unlock_mapping(struct address_space *mapping)
+{
+}
+
 void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
 {
        truncate_inode_pages_range(inode->i_mapping, lstart, lend);

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 824676a..cb33d9c 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -636,7 +636,7 @@ redo:
                 * When racing with an mlock or AS_UNEVICTABLE clearing
                 * (page is unlocked) make sure that if the other thread
                 * does not observe our setting of PG_lru and fails
-                * isolation/check_move_unevictable_page,
+                * isolation/check_move_unevictable_pages,
                 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
                 * the page back to the evictable list.
                 *
@@ -3355,104 +3355,56 @@ int page_evictable(struct page *page, struct vm_area_struct *vma)
 
 #ifdef CONFIG_SHMEM
 /**
- * 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
+ * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
+ * @pages:     array of pages to check
+ * @nr_pages:  number of pages to check
  *
- * 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.
+ * Checks pages for evictability and moves them to the appropriate lru list.
  *
  * This function is only used for SysV IPC SHM_UNLOCK.
  */
-static void check_move_unevictable_page(struct page *page, struct zone *zone)
+void check_move_unevictable_pages(struct page **pages, int nr_pages)
 {
-       VM_BUG_ON(PageActive(page));
+       struct zone *zone = NULL;
+       int pgscanned = 0;
+       int pgrescued = 0;
+       int i;
 
-retry:
-       ClearPageUnevictable(page);
-       if (page_evictable(page, NULL)) {
-               enum lru_list l = page_lru_base_type(page);
+       for (i = 0; i < nr_pages; i++) {
+               struct page *page = pages[i];
+               struct zone *pagezone;
 
-               __dec_zone_state(zone, NR_UNEVICTABLE);
-               list_move(&page->lru, &zone->lru[l].list);
-               mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
-               __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);
-               mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
-               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.
- *
- * This function is only used for SysV IPC SHM_UNLOCK.
- */
-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;
+               pgscanned++;
+               pagezone = page_zone(page);
+               if (pagezone != zone) {
+                       if (zone)
+                               spin_unlock_irq(&zone->lru_lock);
+                       zone = pagezone;
+                       spin_lock_irq(&zone->lru_lock);
+               }
 
-       if (mapping->nrpages == 0)
-               return;
+               if (!PageLRU(page) || !PageUnevictable(page))
+                       continue;
 
-       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 (page_evictable(page, NULL)) {
+                       enum lru_list lru = page_lru_base_type(page);
 
-                       if (PageLRU(page) && PageUnevictable(page))
-                               check_move_unevictable_page(page, zone);
+                       VM_BUG_ON(PageActive(page));
+                       ClearPageUnevictable(page);
+                       __dec_zone_state(zone, NR_UNEVICTABLE);
+                       list_move(&page->lru, &zone->lru[lru].list);
+                       mem_cgroup_move_lists(page, LRU_UNEVICTABLE, lru);
+                       __inc_zone_state(zone, NR_INACTIVE_ANON + lru);
+                       pgrescued++;
                }
-               if (zone)
-                       spin_unlock_irq(&zone->lru_lock);
-               pagevec_release(&pvec);
+       }
 
-               count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
-               cond_resched();
+       if (zone) {
+               __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
+               __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
+               spin_unlock_irq(&zone->lru_lock);
        }
 }
-#else
-void scan_mapping_unevictable_pages(struct address_space *mapping)
-{
-}
 #endif /* CONFIG_SHMEM */
 
 static void warn_scan_unevictable_pages(void)