[PATCH] mm/page_alloc: Wait for oom_lock before retrying.

[Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>]

If the OOM killer is invoked when many threads are looping inside the
page allocator, it is possible that the OOM killer is preempted by other
threads. 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.

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 mm/page_alloc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 51cbe1e..e5c1102 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3060,6 +3060,7 @@ void warn_alloc(gfp_t gfp_mask, const char *fmt, ...)
 		.order = order,
 	};
 	struct page *page;
+	static bool wait_more;
 
 	*did_some_progress = 0;
 
@@ -3070,6 +3071,9 @@ void warn_alloc(gfp_t gfp_mask, const char *fmt, ...)
 	if (!mutex_trylock(&oom_lock)) {
 		*did_some_progress = 1;
 		schedule_timeout_uninterruptible(1);
+		while (wait_more)
+			if (schedule_timeout_killable(1) < 0)
+				break;
 		return NULL;
 	}
 
@@ -3109,6 +3113,7 @@ void warn_alloc(gfp_t gfp_mask, const char *fmt, ...)
 		if (gfp_mask & __GFP_THISNODE)
 			goto out;
 	}
+	wait_more = true;
 	/* Exhausted what can be done so it's blamo time */
 	if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
 		*did_some_progress = 1;
@@ -3125,6 +3130,7 @@ void warn_alloc(gfp_t gfp_mask, const char *fmt, ...)
 					ALLOC_NO_WATERMARKS, ac);
 		}
 	}
+	wait_more = false;
 out:
 	mutex_unlock(&oom_lock);
 	return page;
-- 
1.8.3.1

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>