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SHM_UNLOCK: fix long unpreemptible section

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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>
This commit is contained in:
Hugh Dickins
2012-01-20 14:34:19 -08:00
committed by Linus Torvalds
parent cb78edfdce
commit 85046579bd
3 changed files with 33 additions and 23 deletions
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12
mm/vmscan.c
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@@ -3499,6 +3499,7 @@ int page_evictable(struct page *page, struct vm_area_struct *vma)
return 1;
}
#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
@@ -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)
pagevec_release(&pvec);
count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
cond_resched();
}
}
#else
void scan_mapping_unevictable_pages(struct address_space *mapping)
{
}
#endif /* CONFIG_SHMEM */
static void warn_scan_unevictable_pages(void)
{