linux-kernel - Re: [PATCH] mm: mglru: fix add unevictable folio to lruvec->lists

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Date:   Thu, 14 Sep 2023 21:25:10 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     江志国 <justinjiang@...o.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "opensource.kernel" <opensource.kernel@...o.com>
Subject: Re: [PATCH] mm: mglru: fix add unevictable folio to lruvec->lists

On Thu, Sep 14, 2023 at 9:19 PM 江志国 <justinjiang@...o.com> wrote:
>
> Hi Yu Zhao:
>
> How is the unevictable folio managed in kernel?

https://www.kernel.org/doc/Documentation/vm/unevictable-lru.txt

> On Thu, Sep 14, 2023 at 8:08 AM Zhiguo Jiang <justinjiang@...o.com> wrote:
> >
> > The unevictable folio is not supported to add to lruvec->lists in
> > lruvec_add_folio().
> >
> > So use lruvec_add_folio_tail() instead of lruvec_add_folio() to add
> > unevictable folio to lruvec->lists in sort_folio().
> >
> > Signed-off-by: Zhiguo Jiang <justinjiang@...o.com>
> > ---
> >  mm/vmscan.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)  mode change 100644 =>
> > 100755 mm/vmscan.c
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c index
> > 661615fa709b..a15e45632034
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -4237,7 +4237,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
> >                 success = lru_gen_del_folio(lruvec, folio, true);
> >                 VM_WARN_ON_ONCE_FOLIO(!success, folio);
> >                 folio_set_unevictable(folio);
> > -               lruvec_add_folio(lruvec, folio);
> > +               lruvec_add_folio_tail(lruvec, folio);
> >                 __count_vm_events(UNEVICTABLE_PGCULLED, delta);
> >                 return true;
> >         }
>
> NAK.
>
> lruvec_add_folio()
> {
>         ...
>
>         if (lru != LRU_UNEVICTABLE)
>                 list_add(&folio->lru, &lruvec->lists[lru]); }
>
> lruvec_add_folio_tail()
> {
>         ...
>
>         /* This is not expected to be used on LRU_UNEVICTABLE */
>         list_add_tail(&folio->lru, &lruvec->lists[lru]); }
>
> struct page {
>         ...
>                         union {
>                                 struct list_head lru;
>
>                                 /* Or, for the Unevictable "LRU list" slot */
>                                 struct {
>         ...
> }