linux-kernel - Re: [PATCH 4/9] mm/z3fold: throw warning on failure of trylock_page in z3fold

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Date:   Thu, 19 May 2022 09:10:03 +0200
From:   Vitaly Wool <vitaly.wool@...sulko.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/9] mm/z3fold: throw warning on failure of trylock_page
 in z3fold_alloc

On Fri, Apr 29, 2022 at 8:40 AM Miaohe Lin <linmiaohe@...wei.com> wrote:
>
> If trylock_page fails, the page won't be non-lru movable page. When this
> page is freed via free_z3fold_page, it will trigger bug on PageMovable
> check in __ClearPageMovable. Throw warning on failure of trylock_page to
> guard against such rare case just as what zsmalloc does.

I don't see how this is better than what we currently have. We can
check if a page is movable before calling __ClearPageMovable instead.

~Vitaly

> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/z3fold.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 4e6814c5694f..b3b4e65c107f 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1122,10 +1122,9 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
>                 __SetPageMovable(page, pool->inode->i_mapping);
>                 unlock_page(page);
>         } else {
> -               if (trylock_page(page)) {
> -                       __SetPageMovable(page, pool->inode->i_mapping);
> -                       unlock_page(page);
> -               }
> +               WARN_ON(!trylock_page(page));
> +               __SetPageMovable(page, pool->inode->i_mapping);
> +               unlock_page(page);
>         }
>         z3fold_page_lock(zhdr);
>
> --
> 2.23.0
>