Re: [PATCH] mm: page_alloc: dump migrate-failed pages only at -EBUSY

[David Hildenbrand <david@redhat.com>]

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Minchan Kim <minchan@kernel.org> schrieb am Do. 20. Mai 2021 um 21:20:

> On Wed, May 19, 2021 at 02:33:41PM -0700, Minchan Kim wrote:
> > alloc_contig_dump_pages aims for helping debugging page migration
> > failure by page refcount mismatch or something else of page itself
> > from migration handler function. However, in -ENOMEM case, there is
> > nothing to get clue from page descriptor information so just
> > dump pages only when -EBUSY happens.
> >
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  mm/page_alloc.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 3100fcb08500..c0a2971dc755 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -8760,7 +8760,8 @@ static int __alloc_contig_migrate_range(struct
> compact_control *cc,
> >
> >       lru_cache_enable();
> >       if (ret < 0) {
> > -             alloc_contig_dump_pages(&cc->migratepages);
> > +             if (ret == -EBUSY)
> > +                     alloc_contig_dump_pages(&cc->migratepages);
> >               putback_movable_pages(&cc->migratepages);
> >               return ret;
> >       }
> > --
> > 2.31.1.751.gd2f1c929bd-goog
> >
>
> Resend with a little modifying description.
>
> From c5a2fea291cf46079b87cc9ac9a25fc7f819d0fd Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@kernel.org>
> Date: Wed, 19 May 2021 14:22:18 -0700
> Subject: [PATCH] mm: page_alloc: dump migrate-failed pages only at -EBUSY
>
> alloc_contig_dump_pages aims for helping debugging page migration
> failure by elevated page refcount compared to expected_count.
> (for the detail, please look at migrate_page_move_mapping)
>
> However, -ENOMEM is just the case that system is under memory
> pressure state, not relevant with page refcount at all. Thus,
> the dumping page list is not helpful for the debugging point of view.
>

what about -ENOMEM when migrating empty/free huge pages? I think there is
value in having the pages dumped to identify something like that. And it
doesn‘t require heavy memory pressure to fail allocating a huge page.


> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  mm/page_alloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3100fcb08500..c0a2971dc755 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8760,7 +8760,8 @@ static int __alloc_contig_migrate_range(struct
> compact_control *cc,
>
>         lru_cache_enable();
>         if (ret < 0) {
> -               alloc_contig_dump_pages(&cc->migratepages);
> +               if (ret == -EBUSY)
> +                       alloc_contig_dump_pages(&cc->migratepages);
>                 putback_movable_pages(&cc->migratepages);
>                 return ret;
>         }
> --
> 2.31.1.818.g46aad6cb9e-goog
>
> --
Thanks,

David / dhildenb

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