linux-kernel - Re: [PATCH] mm/z3fold.c: remove z3fold

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Date:   Wed, 10 Jul 2019 14:51:16 -0700
From:   Henry Burns <henryburns@...gle.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Vitaly Wool <vitalywool@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vitaly Vul <vitaly.vul@...y.com>,
        Jonathan Adams <jwadams@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Snild Dolkow <snild@...y.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/z3fold.c: remove z3fold_migration trylock

> > z3fold_page_migrate() will never succeed because it attempts to acquire a
> > lock that has already been taken by migrate.c in __unmap_and_move().
> >
> > __unmap_and_move() migrate.c
> >   trylock_page(oldpage)
> >   move_to_new_page(oldpage_newpage)
> >     a_ops->migrate_page(oldpage, newpage)
> >       z3fold_page_migrate(oldpage, newpage)
> >         trylock_page(oldpage)
> >
> >
> > Signed-off-by: Henry Burns <henryburns@...gle.com>
>
> Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
>
> Please add the Fixes tag as well.
Fixes: 1f862989b04a ("mm/z3fold.c: support page migration")
>
> > ---
> >  mm/z3fold.c | 6 ------
> >  1 file changed, 6 deletions(-)
> >
> > diff --git a/mm/z3fold.c b/mm/z3fold.c
> > index 985732c8b025..9fe9330ab8ae 100644
> > --- a/mm/z3fold.c
> > +++ b/mm/z3fold.c
> > @@ -1335,16 +1335,11 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
> >         zhdr = page_address(page);
> >         pool = zhdr_to_pool(zhdr);
> >
> > -       if (!trylock_page(page))
> > -               return -EAGAIN;
> > -
> >         if (!z3fold_page_trylock(zhdr)) {
> > -               unlock_page(page);
> >                 return -EAGAIN;
> >         }
> >         if (zhdr->mapped_count != 0) {
> >                 z3fold_page_unlock(zhdr);
> > -               unlock_page(page);
> >                 return -EBUSY;
> >         }
> >         new_zhdr = page_address(newpage);
> > @@ -1376,7 +1371,6 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
> >         queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
> >
> >         page_mapcount_reset(page);
> > -       unlock_page(page);
> >         put_page(page);
> >         return 0;
> >  }
> > --
> > 2.22.0.410.gd8fdbe21b5-goog
> >