path: root/mm
diff options
authorHugh Dickins <hughd@google.com>2012-01-20 14:34:19 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-23 08:38:48 -0800
commit85046579bde15e532983438f86b36856e358f417 (patch)
tree9b80b31791e63520277617a5abe85692dc480cd0 /mm
parentcb78edfdcef5259ac9e9088bd63810d21299928d (diff)
SHM_UNLOCK: fix long unpreemptible section
scan_mapping_unevictable_pages() is used to make SysV SHM_LOCKed pages evictable again once the shared memory is unlocked. It does this with pagevec_lookup()s across the whole object (which might occupy most of memory), and takes 300ms to unlock 7GB here. A cond_resched() every PAGEVEC_SIZE pages would be good. However, KOSAKI-san points out that this is called under shmem.c's info->lock, and it's also under shm.c's shm_lock(), both spinlocks. There is no strong reason for that: we need to take these pages off the unevictable list soonish, but those locks are not required for it. So move the call to scan_mapping_unevictable_pages() from shmem.c's unlock handling up to shm.c's unlock handling. Remove the recently added barrier, not needed now we have spin_unlock() before the scan. Use get_file(), with subsequent fput(), to make sure we have a reference to mapping throughout scan_mapping_unevictable_pages(): that's something that was previously guaranteed by the shm_lock(). Remove shmctl's lru_add_drain_all(): we don't fault in pages at SHM_LOCK time, and we lazily discover them to be Unevictable later, so it serves no purpose for SHM_LOCK; and serves no purpose for SHM_UNLOCK, since pages still on pagevec are not marked Unevictable. The original code avoided redundant rescans by checking VM_LOCKED flag at its level: now avoid them by checking shp's SHM_LOCKED. The original code called scan_mapping_unevictable_pages() on a locked area at shm_destroy() time: perhaps we once had accounting cross-checks which required that, but not now, so skip the overhead and just let inode eviction deal with them. Put check_move_unevictable_page() and scan_mapping_unevictable_pages() under CONFIG_SHMEM (with stub for the TINY case when ramfs is used), more as comment than to save space; comment them used for SHM_UNLOCK. 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>
Diffstat (limited to 'mm')
2 files changed, 11 insertions, 8 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index feead1943d92..4aaa53abe302 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1068,13 +1068,6 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
user_shm_unlock(inode->i_size, user);
info->flags &= ~VM_LOCKED;
- /*
- * Ensure that a racing putback_lru_page() can see
- * the pages of this mapping are evictable when we
- * skip them due to !PageLRU during the scan.
- */
- smp_mb__after_clear_bit();
- scan_mapping_unevictable_pages(file->f_mapping);
retval = 0;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2880396f7953..e097c1026b58 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3499,6 +3499,7 @@ 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
@@ -3509,6 +3510,8 @@ int page_evictable(struct page *page, struct vm_area_struct *vma)
* Restrictions: zone->lru_lock must be held, page must be on LRU and must
* have PageUnevictable set.
+ *
+ * This function is only used for SysV IPC SHM_UNLOCK.
static void check_move_unevictable_page(struct page *page, struct zone *zone)
@@ -3545,6 +3548,8 @@ retry:
* 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)
@@ -3590,9 +3595,14 @@ void scan_mapping_unevictable_pages(struct address_space *mapping)
count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
+ cond_resched();
+void scan_mapping_unevictable_pages(struct address_space *mapping)
+#endif /* CONFIG_SHMEM */
static void warn_scan_unevictable_pages(void)