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

[David Hildenbrand]

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@xxxxxxxxxx>
> ---
>   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@xxxxxxxxxx>

--
Thanks,

David / dhildenb