patches/old/shmem-skip-page-split-if-were-not-reclaiming.patch

From: Luis Chamberlain <mcgrof@kernel.org>
Subject: shmem: skip page split if we're not reclaiming
Date: Thu, 9 Mar 2023 15:05:43 -0800

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.

Link: https://lkml.kernel.org/r/20230309230545.2930737-5-mcgrof@kernel.org
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Tested-by: Xin Hao <xhao@linux.alibaba.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Adam Manzanares <a.manzanares@samsung.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/mm/shmem.c~shmem-skip-page-split-if-were-not-reclaiming
+++ a/mm/shmem.c
@@ -1357,6 +1357,12 @@ static int shmem_writepage(struct page *
 	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 "always" or
 	 * "force", drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages,
@@ -1372,10 +1378,6 @@ static int shmem_writepage(struct page *
 	}
 
 	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
_