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References: <20230309230545.2930737-1-mcgrof@kernel.org> <20230309230545.2930737-5-mcgrof@kernel.org>
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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Thu, 9 Mar 2023 15:09:01 -0800
Message-ID: <CAJD7tka+4gaEUHWcUQu9fgLrGmuoZDb3Yp7GT4fv=Tzrwobd4g@mail.gmail.com>
Subject: Re: [PATCH v2 4/6] shmem: skip page split if we're not reclaiming
To:     Luis Chamberlain <mcgrof@kernel.org>
Cc:     hughd@google.com, akpm@linux-foundation.org, willy@infradead.org,
        brauner@kernel.org, linux-mm@kvack.org, p.raghav@samsung.com,
        da.gomez@samsung.com, a.manzanares@samsung.com, dave@stgolabs.net,
        keescook@chromium.org, patches@lists.linux.dev,
        linux-kernel@vger.kernel.org, David Hildenbrand <david@redhat.com>
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On Thu, Mar 9, 2023 at 3:05=E2=80=AFPM Luis Chamberlain <mcgrof@kernel.org>=
 wrote:
>
> In theory when info->flags & VM_LOCKED we should not be getting
> shem_writepage() called so we should be verifying this with a
> WARN_ON_ONCE(). Since we should not be swapping then best to ensure
> we also don't do the folio split earlier too. So just move the check
> early to avoid folio splits in case its a dubious call.
>
> We also have a similar early bail when !total_swap_pages so just move
> that earlier to avoid the possible folio split in the same situation.
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>

> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>  mm/shmem.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 68e9970baf1e..dfd995da77b4 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1350,6 +1350,12 @@ static int shmem_writepage(struct page *page, stru=
ct writeback_control *wbc)
>         if (WARN_ON_ONCE(!wbc->for_reclaim))
>                 goto redirty;
>
> +       if (WARN_ON_ONCE(info->flags & VM_LOCKED))
> +               goto redirty;
> +
> +       if (!total_swap_pages)
> +               goto redirty;
> +
>         /*
>          * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "alway=
s" or
>          * "force", drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge p=
ages,
> @@ -1365,10 +1371,6 @@ static int shmem_writepage(struct page *page, stru=
ct writeback_control *wbc)
>         }
>
>         index =3D folio->index;
> -       if (info->flags & VM_LOCKED)
> -               goto redirty;
> -       if (!total_swap_pages)
> -               goto redirty;
>
>         /*
>          * This is somewhat ridiculous, but without plumbing a SWAP_MAP_F=
ALLOC
> --
> 2.39.1
>