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

[Shakeel Butt]

On Thu, Mar 15, 2018 at 9:45 AM, Andrey Ryabinin
<aryabinin@xxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxxxxx>

Indeed I am seeing oom-kills without the patch.

Tested-by: Shakeel Butt <shakeelb@xxxxxxxxxx>

> Cc: <stable@xxxxxxxxxxxxxxx>
> ---
>  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
>
> --
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