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

[Kairui Song <ryncsn@gmail.com>]

On Sat, Aug 31, 2024 at 8:38 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 29 Aug 2024 18:25:43 +0800 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
> >
> > ...
> >
> > 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.
>
> Thanks, I'll queue this for testing and review.  Could people please
> consider whether we should backport this into -stable kernels.
>

Hi Andrew, Thanks for picking this up.

> > 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]
>
> This one is already queued for -stable.

I didn't see this in -unstable or -stable though, is there any other
repo or branch I missed? Jingxiang is referring to this fix from Yu:

diff --git a/mm/vmscan.c b/mm/vmscan.c
index cfa839284b92..778bf5b7ef97 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4320,7 +4320,7 @@ static bool sort_folio(struct lruvec *lruvec,
struct folio *folio, struct scan_c
        }

        /* ineligible */
-       if (zone > sc->reclaim_idx || skip_cma(folio, sc)) {
+       if (!folio_test_lru(folio) || zone > sc->reclaim_idx ||
skip_cma(folio, sc)) {
                gen = folio_inc_gen(lruvec, folio, false);
                list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
                return true;