On 12/07/2016 04:29 PM, Tetsuo Handa wrote:
As a result, the OOM killer is unable to send SIGKILL to OOM
victims and/or wake up the OOM reaper by releasing oom_lock for minutes
because other threads consume a lot of CPU time for pointless direct
reclaim.
----------
[ 2802.635229] Killed process 7267 (a.out) total-vm:4176kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB
[ 2802.644296] oom_reaper: reaped process 7267 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
[ 2802.650237] Out of memory: Kill process 7268 (a.out) score 999 or sacrifice child
[ 2803.653052] Killed process 7268 (a.out) total-vm:4176kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB
[ 2804.426183] oom_reaper: reaped process 7268 (a.out), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
[ 2804.432524] Out of memory: Kill process 7269 (a.out) score 999 or sacrifice child
[ 2805.349380] a.out: page allocation stalls for 10047ms, order:0, mode:0x24280ca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO)
[ 2805.349383] CPU: 2 PID: 7243 Comm: a.out Not tainted 4.9.0-rc8 #62
(...snipped...)
[ 3540.977499] a.out 7269 22716.893359 5272 120
[ 3540.977499] 0.000000 1447.601063 0.000000
[ 3540.977499] 0 0
[ 3540.977500] /autogroup-155
----------
This patch adds extra sleeps which is effectively equivalent to
if (mutex_lock_killable(&oom_lock) == 0)
mutex_unlock(&oom_lock);
before retrying allocation at __alloc_pages_may_oom() so that the
OOM killer is not preempted by other threads waiting for the OOM
killer/reaper to reclaim memory. Since the OOM reaper grabs oom_lock
due to commit e2fe14564d3316d1 ("oom_reaper: close race with exiting
task"), waking up other threads before the OOM reaper is woken up by
directly waiting for oom_lock might not help so much.
So, why don't you simply s@mutex_trylock@mutex_lock_killable@ then?
The trylock is simply an optimistic heuristic to retry while the memory
is being freed. Making this part sync might help for the case you are
seeing.
May I? Something like below? With patch below, the OOM killer can send
SIGKILL smoothly and printk() can report smoothly (the frequency of
"** XXX printk messages dropped **" messages is significantly reduced).
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2c6d5f6..ee0105b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3075,7 +3075,7 @@ void warn_alloc(gfp_t gfp_mask, const char *fmt, ...)
* Acquire the oom lock. If that fails, somebody else is
* making progress for us.
*/
The comment above could use some updating then. Although maybe "somebody
killed us" is also technically "making progress for us" :)
- if (!mutex_trylock(&oom_lock)) {
+ if (mutex_lock_killable(&oom_lock)) {
*did_some_progress = 1;
schedule_timeout_uninterruptible(1);
I think if we get here, it means somebody killed us, so we should not do
this uninterruptible sleep anymore? (maybe also the caller could need
some check to expedite the kill?).
return NULL;
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