* + memcg-fix-race-in-file_mapped-accouting-flag-management.patch added to -mm tree
@ 2010-09-13 22:48 akpm
0 siblings, 0 replies; only message in thread
From: akpm @ 2010-09-13 22:48 UTC (permalink / raw)
To: mm-commits; +Cc: kamezawa.hiroyu, balbir, gthelen, nishimura
The patch titled
memcg: fix race in file_mapped accouting flag management
has been added to the -mm tree. Its filename is
memcg-fix-race-in-file_mapped-accouting-flag-management.patch
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Subject: memcg: fix race in file_mapped accouting flag management
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Presently memory cgroup accounts file-mapped by counter and flag. counter
is working in the same way with zone_stat but FileMapped flag only exists
in memcg (for helping move_account).
This flag can be updated wrongly in a case. Assume CPU0 and CPU1 and a
thread mapping a page on CPU0, another thread unmapping it on CPU1.
CPU0 CPU1
rmv rmap (mapcount 1->0)
add rmap (mapcount 0->1)
lock_page_cgroup()
memcg counter+1 (some delay)
set MAPPED FLAG.
unlock_page_cgroup()
lock_page_cgroup()
memcg counter-1
clear MAPPED flag
In above sequence, counter is properly updated but FLAG is not. This
means that representing a state by a flag which is maintained by counter
needs some specail care.
To handle this, at claering a flag, this patch check mapcount directly and
clear the flag only when mapcount == 0. (if mapcount >0, someone will
make it to zero later and flag will be cleared.)
Reverse case, dec-after-inc cannot be a problem because page_table_lock()
works well for it. (IOW, to make above sequence, 2 processes should touch
the same page at once with map/unmap.)
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/memcontrol.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN mm/memcontrol.c~memcg-fix-race-in-file_mapped-accouting-flag-management mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-fix-race-in-file_mapped-accouting-flag-management
+++ a/mm/memcontrol.c
@@ -1485,7 +1485,8 @@ void mem_cgroup_update_file_mapped(struc
SetPageCgroupFileMapped(pc);
} else {
__this_cpu_dec(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
- ClearPageCgroupFileMapped(pc);
+ if (!page_mapped(page)) /* for race between dec->inc counter */
+ ClearPageCgroupFileMapped(pc);
}
done:
_
Patches currently in -mm which might be from kamezawa.hiroyu@jp.fujitsu.com are
oom-always-return-a-badness-score-of-non-zero-for-eligible-tasks.patch
vfs-introduce-fmode_neg_offset-for-allowing-negative-f_pos.patch
vfs-introduce-fmode_neg_offset-for-allowing-negative-f_pos-fix.patch
vmscan-do-not-writeback-filesystem-pages-in-direct-reclaim.patch
vmscan-kick-flusher-threads-to-clean-pages-when-reclaim-is-encountering-dirty-pages.patch
oom-add-per-mm-oom-disable-count.patch
oom-avoid-killing-a-task-if-a-thread-sharing-its-mm-cannot-be-killed.patch
oom-kill-all-threads-sharing-oom-killed-tasks-mm.patch
oom-kill-all-threads-sharing-oom-killed-tasks-mm-fix.patch
oom-kill-all-threads-sharing-oom-killed-tasks-mm-fix-fix.patch
oom-rewrite-error-handling-for-oom_adj-and-oom_score_adj-tunables.patch
oom-fix-locking-for-oom_adj-and-oom_score_adj.patch
memory-hotplug-fix-notifiers-return-value-check.patch
memory-hotplug-unify-is_removable-and-offline-detection-code.patch
memory-hotplug-unify-is_removable-and-offline-detection-code-checkpatch-fixes.patch
memcg-fix-race-in-file_mapped-accouting-flag-management.patch
memcg-avoid-lock-in-updating-file_mapped-was-fix-race-in-file_mapped-accouting-flag-management.patch
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2010-09-13 22:48 + memcg-fix-race-in-file_mapped-accouting-flag-management.patch added to -mm tree akpm
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