linux-kernel - [PATCH] mm/filemap: set folio->mapping to NULL before xas

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Date: Sat, 23 Mar 2024 06:04:54 +0900
From: Soma Nakata <soma.nakata01@...il.com>
To: linux-mm@...ck.org
Cc: soma.nakata01@...il.com,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] mm/filemap: set folio->mapping to NULL before xas_store()

Functions such as __filemap_get_folio() check the truncation of
folios based on the mapping field. Therefore setting this field to NULL
earlier prevents unnecessary operations on already removed folios.

Signed-off-by: Soma Nakata <soma.nakata01@...il.com>
---
 mm/filemap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 2723104cc06a..79bac7c00084 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -139,11 +139,12 @@ static void page_cache_delete(struct address_space *mapping,
 
 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
+	folio->mapping = NULL;
+	/* Leave page->index set: truncation lookup relies upon it */
+
 	xas_store(&xas, shadow);
 	xas_init_marks(&xas);
 
-	folio->mapping = NULL;
-	/* Leave page->index set: truncation lookup relies upon it */
 	mapping->nrpages -= nr;
 }
 
-- 
2.25.1