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@kernel.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
-- 
2.39.1

On Thu, Mar 2, 2023 at 3:28 PM 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.
>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

Reviewed-by: Yosry Ahmed <yosryahmed@google.com>

> ---
>  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
>

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@kernel.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@redhat.com>

-- 
Thanks,

David / dhildenb