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SubjectRe: [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 <gthelen@google.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

--
Kirill A. Shutemov


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