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List:       linux-api
Subject:    Re: [PATCH 03/16] huge tmpfs: remove shrinklist addition from shmem_setattr()
From:       Yang Shi <shy828301 () gmail ! com>
Date:       2021-07-30 21:50:58
Message-ID: CAHbLzkp9UQ9bb4gMN-BtrSHY3uet+nSxN-wMaObrtp5yhSN5Sw () mail ! gmail ! com
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On Fri, Jul 30, 2021 at 12:31 AM Hugh Dickins <hughd@google.com> wrote:
>
> There's a block of code in shmem_setattr() to add the inode to
> shmem_unused_huge_shrink()'s shrinklist when lowering i_size: it dates
> from before 5.7 changed truncation to do split_huge_page() for itself,
> and should have been removed at that time.
>
> I am over-stating that: split_huge_page() can fail (notably if there's
> an extra reference to the page at that time), so there might be value in
> retrying.  But there were already retries as truncation worked through
> the tails, and this addition risks repeating unsuccessful retries
> indefinitely: I'd rather remove it now, and work on reducing the
> chance of split_huge_page() failures separately, if we need to.

Yes, agreed. Reviewed-by: Yang Shi <shy828301@gmail.com>

>
> Fixes: 71725ed10c40 ("mm: huge tmpfs: try to split_huge_page() when punching hole")
> Signed-off-by: Hugh Dickins <hughd@google.com>
> ---
>  mm/shmem.c | 19 -------------------
>  1 file changed, 19 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 24c9da6b41c2..ce3ccaac54d6 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1061,7 +1061,6 @@ static int shmem_setattr(struct user_namespace *mnt_userns,
>  {
>         struct inode *inode = d_inode(dentry);
>         struct shmem_inode_info *info = SHMEM_I(inode);
> -       struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
>         int error;
>
>         error = setattr_prepare(&init_user_ns, dentry, attr);
> @@ -1097,24 +1096,6 @@ static int shmem_setattr(struct user_namespace *mnt_userns,
>                         if (oldsize > holebegin)
>                                 unmap_mapping_range(inode->i_mapping,
>                                                         holebegin, 0, 1);
> -
> -                       /*
> -                        * Part of the huge page can be beyond i_size: subject
> -                        * to shrink under memory pressure.
> -                        */
> -                       if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
> -                               spin_lock(&sbinfo->shrinklist_lock);
> -                               /*
> -                                * _careful to defend against unlocked access to
> -                                * ->shrink_list in shmem_unused_huge_shrink()
> -                                */
> -                               if (list_empty_careful(&info->shrinklist)) {
> -                                       list_add_tail(&info->shrinklist,
> -                                                       &sbinfo->shrinklist);
> -                                       sbinfo->shrinklist_len++;
> -                               }
> -                               spin_unlock(&sbinfo->shrinklist_lock);
> -                       }
>                 }
>         }
>
> --
> 2.26.2
>
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