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memcg: fix multiple large threshold notifications 

A memory cgroup with (1) multiple threshold notifications and (2) at least
one threshold >=2G was not reliable.  Specifically the notifications would
either not fire or would not fire in the proper order.

The __mem_cgroup_threshold() signaling logic depends on keeping 64 bit
thresholds in sorted order.  mem_cgroup_usage_register_event() sorts them
with compare_thresholds(), which returns the difference of two 64 bit
thresholds as an int.  If the difference is positive but has bit[31] set,
then sort() treats the difference as negative and breaks sort order.

This fix compares the two arbitrary 64 bit thresholds returning the
classic -1, 0, 1 result.

The test below sets two notifications (at 0x1000 and 0x81001000):
  cd /sys/fs/cgroup/memory
  mkdir x
  for x in 4096 2164264960; do
    cgroup_event_listener x/memory.usage_in_bytes $x | sed "s/^/$x listener:/" &
  done
  echo $$ > x/cgroup.procs
  anon_leaker 500M

v3.11-rc7 fails to signal the 4096 event listener:
  Leaking...
  Done leaking pages.

Patched v3.11-rc7 properly notifies:
  Leaking...
  4096 listener:2013:8:31:14:13:36
  Done leaking pages.

The fixed bug is old.  It appears to date back to the introduction of
memcg threshold notifications in v2.6.34-rc1-116-g2e72b6347c94 "memcg:
implement memory thresholds"

Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Greg Thelen 2013-09-11 14:23:08 -07:00 committed by Linus Torvalds
parent 7b5219db00
commit 2bff24a370
1 changed files with 7 additions and 1 deletions
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8
mm/memcontrol.c
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@ -5591,7 +5591,13 @@ static int compare_thresholds(const void *a, const void *b)
const struct mem_cgroup_threshold *_a = a; const struct mem_cgroup_threshold *_a = a;
const struct mem_cgroup_threshold *_b = b; const struct mem_cgroup_threshold *_b = b;
return _a->threshold - _b->threshold; if (_a->threshold > _b->threshold)
return 1;
if (_a->threshold < _b->threshold)
return -1;
return 0;
} }
static int mem_cgroup_oom_notify_cb(struct mem_cgroup *memcg) static int mem_cgroup_oom_notify_cb(struct mem_cgroup *memcg)