LinuxLists.cc - [PATCH] memcg: fix multiple large threshold notifications

2013-09-01 00:06:53

Subject: [PATCH] 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 <[email protected]>
---
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

2013-09-03 10:01:22

by Michal Hocko

[permalink] [raw]

Subject: Re: [PATCH] memcg: fix multiple large threshold notifications

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 <[email protected]>

Acked-by: Michal Hocko <[email protected]>

I guess this qualifies to the stable tree.

Thanks!

> ---
> 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

2013-09-03 22:35:31

by Johannes Weiner

[permalink] [raw]

Subject: Re: [PATCH] memcg: fix multiple large threshold notifications

On Sat, Aug 31, 2013 at 05:06:42PM -0700, 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 <[email protected]>

Acked-by: Johannes Weiner <[email protected]>

2013-09-03 22:43:05

by Kirill A. Shutemov

[permalink] [raw]