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

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Date:   Wed, 10 Jul 2019 14:39:55 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Henry Burns <henryburns@...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

On Wed, Jul 10, 2019 at 2:32 PM Henry Burns <henryburns@...gle.com> wrote:
>
> 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.

> ---
>  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
>