linux-kernel - Re: [PATCH 3/9] mm/z3fold: remove buggy use of stale list for allocation

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Date:   Thu, 19 May 2022 09:06:17 +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 3/9] mm/z3fold: remove buggy use of stale list for allocation

On Fri, Apr 29, 2022 at 8:41 AM Miaohe Lin <linmiaohe@...wei.com> wrote:
>
> Currently if z3fold couldn't find an unbuddied page it would first try to
> pull a page off the stale list. But this approach is problematic. If init
> z3fold page fails later, the page should be freed via free_z3fold_page to
> clean up the relevant resource instead of using __free_page directly. And
> if page is successfully reused, it will BUG_ON later in __SetPageMovable
> because it's already non-lru movable page, i.e. PAGE_MAPPING_MOVABLE is
> already set in page->mapping. In order to fix all of these issues, we can
> simply remove the buggy use of stale list for allocation because can_sleep
> should always be false and we never really hit the reusing code path now.
>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/z3fold.c | 23 +----------------------
>  1 file changed, 1 insertion(+), 22 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 5d8c21f2bc59..4e6814c5694f 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1102,28 +1102,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
>                 bud = FIRST;
>         }
>
> -       page = NULL;
> -       if (can_sleep) {
> -               spin_lock(&pool->stale_lock);
> -               zhdr = list_first_entry_or_null(&pool->stale,
> -                                               struct z3fold_header, buddy);
> -               /*
> -                * Before allocating a page, let's see if we can take one from
> -                * the stale pages list. cancel_work_sync() can sleep so we
> -                * limit this case to the contexts where we can sleep
> -                */
> -               if (zhdr) {
> -                       list_del(&zhdr->buddy);
> -                       spin_unlock(&pool->stale_lock);
> -                       cancel_work_sync(&zhdr->work);
> -                       page = virt_to_page(zhdr);
> -               } else {
> -                       spin_unlock(&pool->stale_lock);
> -               }
> -       }
> -       if (!page)
> -               page = alloc_page(gfp);
> -
> +       page = alloc_page(gfp);
>         if (!page)
>                 return -ENOMEM;

Reviewed-by: Vitaly Wool <vitaly.wool@...sulko.com>
> --
> 2.23.0
>