[PATCH 1/6] mm/vmscan: Wake up flushers for legacy cgroups too

Andrey Ryabinin
2018-03-15T16:45:48Z

Commit 726d061fbd36 ("mm: vmscan: kick flushers when we encounter
dirty pages on the LRU") added flusher invocation to
shrink_inactive_list() when many dirty pages on the LRU are encountered.

However, shrink_inactive_list() doesn't wake up flushers for legacy
cgroup reclaim, so the next commit bbef938429f5 ("mm: vmscan: remove
old flusher wakeup from direct reclaim path") removed the only source
of flusher's wake up in legacy mem cgroup reclaim path.

This leads to premature OOM if there is too many dirty pages in cgroup:
# mkdir /sys/fs/cgroup/memory/test
# echo $$ > /sys/fs/cgroup/memory/test/tasks
# echo 50M > /sys/fs/cgroup/memory/test/memory.limit_in_bytes
# dd if=/dev/zero of=tmp_file bs=1M count=100
Killed

dd invoked oom-killer: gfp_mask=0x14000c0(GFP_KERNEL), nodemask=(null), order=0, oom_score_adj=0

Call Trace:
dump_stack+0x46/0x65
dump_header+0x6b/0x2ac
oom_kill_process+0x21c/0x4a0
out_of_memory+0x2a5/0x4b0
mem_cgroup_out_of_memory+0x3b/0x60
mem_cgroup_oom_synchronize+0x2ed/0x330
pagefault_out_of_memory+0x24/0x54
__do_page_fault+0x521/0x540
page_fault+0x45/0x50

Task in /test killed as a result of limit of /test
memory: usage 51200kB, limit 51200kB, failcnt 73
memory+swap: usage 51200kB, limit 9007199254740988kB, failcnt 0
kmem: usage 296kB, limit 9007199254740988kB, failcnt 0
Memory cgroup stats for /test: cache:49632KB rss:1056KB rss_huge:0KB shmem:0KB
mapped_file:0KB dirty:49500KB writeback:0KB swap:0KB inactive_anon:0KB
active_anon:1168KB inactive_file:24760KB active_file:24960KB unevictable:0KB
Memory cgroup out of memory: Kill process 3861 (bash) score 88 or sacrifice child
Killed process 3876 (dd) total-vm:8484kB, anon-rss:1052kB, file-rss:1720kB, shmem-rss:0kB
oom_reaper: reaped process 3876 (dd), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB

Wake up flushers in legacy cgroup reclaim too.

Fixes: bbef938429f5 ("mm: vmscan: remove old flusher wakeup from direct reclaim path")
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: <stable@vger.kernel.org>
---
mm/vmscan.c | 31 ++++++++++++++++---------------
1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8fcd9f8d7390..4390a8d5be41 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1771,6 +1771,20 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
if (stat.nr_writeback && stat.nr_writeback == nr_taken)
set_bit(PGDAT_WRITEBACK, &pgdat->flags);

+ /*
+ * If dirty pages are scanned that are not queued for IO, it
+ * implies that flushers are not doing their job. This can
+ * happen when memory pressure pushes dirty pages to the end of
+ * the LRU before the dirty limits are breached and the dirty
+ * data has expired. It can also happen when the proportion of
+ * dirty pages grows not through writes but through memory
+ * pressure reclaiming all the clean cache. And in some cases,
+ * the flushers simply cannot keep up with the allocation
+ * rate. Nudge the flusher threads in case they are asleep.
+ */
+ if (stat.nr_unqueued_dirty == nr_taken)
+ wakeup_flusher_threads(WB_REASON_VMSCAN);
+
/*
* Legacy memcg will stall in page writeback so avoid forcibly
* stalling here.
@@ -1783,22 +1797,9 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
if (stat.nr_dirty && stat.nr_dirty == stat.nr_congested)
set_bit(PGDAT_CONGESTED, &pgdat->flags);

- /*
- * If dirty pages are scanned that are not queued for IO, it
- * implies that flushers are not doing their job. This can
- * happen when memory pressure pushes dirty pages to the end of
- * the LRU before the dirty limits are breached and the dirty
- * data has expired. It can also happen when the proportion of
- * dirty pages grows not through writes but through memory
- * pressure reclaiming all the clean cache. And in some cases,
- * the flushers simply cannot keep up with the allocation
- * rate. Nudge the flusher threads in case they are asleep, but
- * also allow kswapd to start writing pages during reclaim.
- */
- if (stat.nr_unqueued_dirty == nr_taken) {
- wakeup_flusher_threads(WB_REASON_VMSCAN);
+ /* Allow kswapd to start writing pages during reclaim. */
+ if (stat.nr_unqueued_dirty == nr_taken)
set_bit(PGDAT_DIRTY, &pgdat->flags);
- }

/*
* If kswapd scans pages marked marked for immediate
--
2.16.1