Re: [PATCH] memcg: fix multiple large threshold notifications
From: Michal Hocko <hidden>
Date: 2013-09-03 10:01:22
Also in:
linux-mm, lkml
On Sat 31-08-13 17:06:42, Greg Thelen wrote:
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 <redacted>Acked-by: Michal Hocko <redacted> I guess this qualifies to the stable tree. Thanks!
quoted hunk ↗ jump to hunk
--- mm/memcontrol.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 0878ff7..aa44621 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -5616,7 +5616,13 @@ static int compare_thresholds(const void *a, const void *b) const struct mem_cgroup_threshold *_a = a; 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)-- 1.8.4
-- Michal Hocko SUSE Labs