linux-kernel - Re: [PATCH] mm/vmscan: wake up flushers conditionally to avoid cgroup OOM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAPL-u-ERAfjg+RP01QE1XfvQqPHn4ngKAwb_XZA2Cy8KTsVwg@mail.gmail.com>
Date: Thu, 5 Sep 2024 17:00:40 -0700
From: Wei Xu <weixugc@...gle.com>
To: Jingxiang Zeng <linuszeng@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Yu Zhao <yuzhao@...gle.com>, "T . J . Mercier" <tjmercier@...gle.com>, 
	Kairui Song <kasong@...cent.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmscan: wake up flushers conditionally to avoid cgroup OOM

On Thu, Aug 29, 2024 at 3:25 AM Jingxiang Zeng
<jingxiangzeng.cas@...il.com> wrote:
>
> From: Zeng Jingxiang <linuszeng@...cent.com>
>
> Commit 14aa8b2d5c2e ("mm/mglru: don't sync disk for each aging cycle")
> removed the opportunity to wake up flushers during the MGLRU page
> reclamation process can lead to an increased likelihood of triggering
> OOM when encountering many dirty pages during reclamation on MGLRU.
>
> This leads to premature OOM if there are too many dirty pages in cgroup:
> Killed

Thanks for the patch. We have encountered a similar problem.

>
> dd invoked oom-killer: gfp_mask=0x101cca(GFP_HIGHUSER_MOVABLE|__GFP_WRITE),
> order=0, oom_score_adj=0
>
> Call Trace:
>   <TASK>
>   dump_stack_lvl+0x5f/0x80
>   dump_stack+0x14/0x20
>   dump_header+0x46/0x1b0
>   oom_kill_process+0x104/0x220
>   out_of_memory+0x112/0x5a0
>   mem_cgroup_out_of_memory+0x13b/0x150
>   try_charge_memcg+0x44f/0x5c0
>   charge_memcg+0x34/0x50
>   __mem_cgroup_charge+0x31/0x90
>   filemap_add_folio+0x4b/0xf0
>   __filemap_get_folio+0x1a4/0x5b0
>   ? srso_return_thunk+0x5/0x5f
>   ? __block_commit_write+0x82/0xb0
>   ext4_da_write_begin+0xe5/0x270
>   generic_perform_write+0x134/0x2b0
>   ext4_buffered_write_iter+0x57/0xd0
>   ext4_file_write_iter+0x76/0x7d0
>   ? selinux_file_permission+0x119/0x150
>   ? srso_return_thunk+0x5/0x5f
>   ? srso_return_thunk+0x5/0x5f
>   vfs_write+0x30c/0x440
>   ksys_write+0x65/0xe0
>   __x64_sys_write+0x1e/0x30
>   x64_sys_call+0x11c2/0x1d50
>   do_syscall_64+0x47/0x110
>   entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
>  memory: usage 308224kB, limit 308224kB, failcnt 2589
>  swap: usage 0kB, limit 9007199254740988kB, failcnt 0
>
>   ...
>   file_dirty 303247360
>   file_writeback 0
>   ...
>
> oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null),cpuset=test,
> mems_allowed=0,oom_memcg=/test,task_memcg=/test,task=dd,pid=4404,uid=0
> Memory cgroup out of memory: Killed process 4404 (dd) total-vm:10512kB,
> anon-rss:1152kB, file-rss:1824kB, shmem-rss:0kB, UID:0 pgtables:76kB
> oom_score_adj:0
>
> The flusher wake up was removed to decrease SSD wearing, but if we are
> seeing all dirty folios at the tail of an LRU, not waking up the flusher
> could lead to thrashing easily. So wake it up when a mem cgroups is
> about to OOM due to dirty caches.
>
> MGLRU still suffers OOM issue on latest mm tree, so the test is done
> with another fix merged [1].
>
> Link: https://lore.kernel.org/linux-mm/CAOUHufYi9h0kz5uW3LHHS3ZrVwEq-kKp8S6N-MZUmErNAXoXmw@mail.gmail.com/ [1]
>
> Fixes: 14aa8b2d5c2e ("mm/mglru: don't sync disk for each aging cycle")
> Signed-off-by: Zeng Jingxiang <linuszeng@...cent.com>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---
>  mm/vmscan.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f27792e77a0f..9cd8c42f67cb 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4447,6 +4447,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
>                                 scanned, skipped, isolated,
>                                 type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
>
> +       sc->nr.taken += isolated;
>         /*
>          * There might not be eligible folios due to reclaim_idx. Check the
>          * remaining to prevent livelock if it's not making progress.
> @@ -4919,6 +4920,14 @@ static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc
>         if (try_to_shrink_lruvec(lruvec, sc))
>                 lru_gen_rotate_memcg(lruvec, MEMCG_LRU_YOUNG);
>
> +       /*
> +        * If too many pages failed to evict due to page being dirty,
> +        * memory pressure have pushed dirty pages to oldest gen,
> +        * wake up flusher.
> +        */
> +       if (sc->nr.unqueued_dirty >= sc->nr.taken)

Any reason not to use a strict == check as in shrink_inactive_list()?

Also, this check allows the wakeup of the flusher threads when both
sc->nr.unqueued_dirty and sc->nr.taken are 0, which is undesirable.

If we skip the wakeup for the cases where both counters are 0, then I
think we need to handle the situation where only dirty file pages are
left for reclaim in the oldest gen. This means that
sc->nr.unqueued_dirty needs to be updated in sort_folios() (in
addition to shrink_folio_list()) as well because sort_folios() doesn't
send dirty file pages to shrink_folio_list() for eviction.

> +               wakeup_flusher_threads(WB_REASON_VMSCAN);
> +
>         clear_mm_walk();
>
>         blk_finish_plug(&plug);
> --
> 2.43.5
>