linux-kernel - Re: [PATCH 4/6] shmem: skip page split if we're not reclaiming

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Message-ID: <b8839e28-1189-bb2d-3afe-d21c2d0182c3@redhat.com>
Date:   Mon, 6 Mar 2023 15:02:46 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Luis Chamberlain <mcgrof@...nel.org>, hughd@...gle.com,
        akpm@...ux-foundation.org, willy@...radead.org, brauner@...nel.org
Cc:     linux-mm@...ck.org, p.raghav@...sung.com, da.gomez@...sung.com,
        a.manzanares@...sung.com, dave@...olabs.net, yosryahmed@...gle.com,
        keescook@...omium.org, patches@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] shmem: skip page split if we're not reclaiming

On 03.03.23 00:27, Luis Chamberlain 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.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>   mm/shmem.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index a5a6da51087e..6006dbb7dbcb 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1352,6 +1352,12 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
>   		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 "always" or
>   	 * "force", drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages,
> @@ -1367,10 +1373,6 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
>   	}
>   
>   	index = 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_FALLOC

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb