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

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Date:   Thu, 20 May 2021 13:51:02 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        John Dias <joaodias@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: page_alloc: dump migrate-failed pages only at -EBUSY

On Thu, May 20, 2021 at 09:28:09PM +0200, David Hildenbrand wrote:
> Minchan Kim <minchan@...nel.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@...nel.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@...nel.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.
> 

-ENOMEM means there is no memory to alloate destination page.
How could it help dumping source pages in those case from dump_page
content point of view?