linux-kernel - [PATCH v2 4/6] shmem: skip page split if we're not reclaiming

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Message-Id: <20230309230545.2930737-5-mcgrof@kernel.org>
Date:   Thu,  9 Mar 2023 15:05:43 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     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, mcgrof@...nel.org, patches@...ts.linux.dev,
        linux-kernel@...r.kernel.org, David Hildenbrand <david@...hat.com>
Subject: [PATCH v2 4/6] shmem: skip page split if we're not reclaiming

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.

Acked-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Christian Brauner <brauner@...nel.org>
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 68e9970baf1e..dfd995da77b4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1350,6 +1350,12 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 	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,
@@ -1365,10 +1371,6 @@ 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