Re: [PATCH V3] mm/vmscan: wake up flushers conditionally to avoid cgroup OOM

[Chris Li <chrisl@kernel.org>]

Hi Jingxiang,

I just tested your v3 patch, apply on top of
d675c821b65f0c496df1d33150619b7635827e89("mm-memcontrol-add-per-memcg-pgpgin-pswpin-counter-v2")
with 684826f8271ad97580b138b9ffd462005e470b99(""zram: free secondary
algorithms names") reverted.

Without your v3 patch it can pass the swap stress test in less than 5 mins.
With your V3 patch it is running over 30 minutes and still can't complete.
It does not produce kernel panic though, just extremely slow at the
linking phase.

Here is the top shows:
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+
COMMAND
  33895 ...    20   0    8872   1780   1780 R  99.3   0.0  33:18.70 as
  34115 ...    20   0   10568   4692   2964 R   1.0   0.0   0:00.97
top

V3 also has regression on my swap stress test.

Chris

On Tue, Sep 24, 2024 at 5:14 AM Jingxiang Zeng
<jingxiangzeng.cas@gmail.com> wrote:
>
> From: Zeng Jingxiang <linuszeng@tencent.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
>
> 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.
>
> Link: https://lkml.kernel.org/r/20240829102543.189453-1-jingxiangzeng.cas@gmail.com
> Link: https://lkml.kernel.org/r/20240913084506.3606292-1-jingxiangzeng.cas@gmail.com
> Fixes: 14aa8b2d5c2e ("mm/mglru: don't sync disk for each aging cycle")
> Signed-off-by: Zeng Jingxiang <linuszeng@tencent.com>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> Cc: T.J. Mercier <tjmercier@google.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: Yu Zhao <yuzhao@google.com>
> ---
> Changes from v2:
> - Acquire the lock before calling the folio_check_dirty_writeback
>   function.
> - Link to v2: https://lore.kernel.org/all/20240913084506.3606292-1-jingxiangzeng.cas@gmail.com/
> Changes from v1:
> - Add code to count the number of unqueued_dirty in the sort_folio
>   function.
> - Link to v1: https://lore.kernel.org/all/20240829102543.189453-1-jingxiangzeng.cas@gmail.com/
> ---
>  mm/vmscan.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 749cdc110c74..12c285a96353 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4290,6 +4290,8 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
>         int delta = folio_nr_pages(folio);
>         int refs = folio_lru_refs(folio);
>         int tier = lru_tier_from_refs(refs);
> +       bool dirty = folio_test_dirty(folio);
> +       bool writeback = folio_test_writeback(folio);
>         struct lru_gen_folio *lrugen = &lruvec->lrugen;
>
>         VM_WARN_ON_ONCE_FOLIO(gen >= MAX_NR_GENS, folio);
> @@ -4330,8 +4332,10 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
>         }
>
>         /* waiting for writeback */
> -       if (folio_test_locked(folio) || folio_test_writeback(folio) ||
> -           (type == LRU_GEN_FILE && folio_test_dirty(folio))) {
> +       if (folio_test_locked(folio) || dirty ||
> +           (type == LRU_GEN_FILE && writeback)) {
> +               if (type == LRU_GEN_FILE && dirty && !writeback)
> +                       sc->nr.unqueued_dirty += delta;
>                 gen = folio_inc_gen(lruvec, folio, true);
>                 list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
>                 return true;
> @@ -4448,6 +4452,7 @@ 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.
> @@ -4920,6 +4925,13 @@ 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 in the coldest generation that cannot
> +        * be isolated, wake up flusher.
> +        */
> +       if (sc->nr.unqueued_dirty > sc->nr.taken)
> +               wakeup_flusher_threads(WB_REASON_VMSCAN);
> +
>         clear_mm_walk();
>
>         blk_finish_plug(&plug);
> --
> 2.43.5
>
>