On Tue, 17 Sept 2024 at 00:11, Wei Xu <weixugc@xxxxxxxxxx> wrote:
>
> On Fri, Sep 13, 2024 at 1:45 AM Jingxiang Zeng
> <jingxiangzeng.cas@xxxxxxxxx> wrote:
> >
> > From: Zeng Jingxiang <linuszeng@xxxxxxxxxxx>
> >
> > 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@xxxxxxxxx
> > Fixes: 14aa8b2d5c2e ("mm/mglru: don't sync disk for each aging cycle")
> > Signed-off-by: Zeng Jingxiang <linuszeng@xxxxxxxxxxx>
> > Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> > Cc: T.J. Mercier <tjmercier@xxxxxxxxxx>
> > Cc: Wei Xu <weixugc@xxxxxxxxxx>
> > Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > ---
> > mm/vmscan.c | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 749cdc110c74..ce471d686a88 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -4284,6 +4284,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
> > int tier_idx)
> > {
> > bool success;
> > + bool dirty, writeback;
> > int gen = folio_lru_gen(folio);
> > int type = folio_is_file_lru(folio);
> > int zone = folio_zonenum(folio);
> > @@ -4332,6 +4333,9 @@ 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))) {
> > + folio_check_dirty_writeback(folio, &dirty, &writeback);
>
> We cannot simply call folio_check_dirty_writeback() here because
> folio_check_dirty_writeback() assumes that the folio is locked (e.g.
> see buffer_check_dirty_writeback()).
Thank you for your modification suggestion.
>
> > + if (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 +4925,14 @@ 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)
> > + wakeup_flusher_threads(WB_REASON_VMSCAN);
> > +
>
> The wakeups will be much more often than intended because
> sc->nr.unqueued_dirty includes the drity file pages now, but
> sc->nr.taken doesn't.
When the scan_folios function scans the coldest generation,
when the number of pages that need to be promoted due to
unqueued dirty pages is greater than the number of pages
that can be isolated, the logic here will wake up the flusher
thread.
This condition will indeed be triggered when there
are too many pages in the coldest generation that cannot
be isolated.
I think this condition for triggering the flusher to wake up is
reasonable. Are there any other good trigger conditions?
>
> > clear_mm_walk();
> >
> > blk_finish_plug(&plug);
> > --
> > 2.43.5
> >
