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

From: Yosry Ahmed
Date: Mon Mar 06 2023 - 14:50:59 EST


On Thu, Mar 2, 2023 at 3:28 PM Luis Chamberlain <mcgrof@xxxxxxxxxx> 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>

Reviewed-by: Yosry Ahmed <yosryahmed@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
> --
> 2.39.1
>