linux-kernel - [PATCH v2 2/4] mm/readahead: Limit page cache size in page_cache_ra

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Date: Thu, 27 Jun 2024 10:39:50 +1000
From: Gavin Shan <gshan@...hat.com>
To: linux-mm@...ck.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	david@...hat.com,
	willy@...radead.org,
	akpm@...ux-foundation.org,
	ryan.roberts@....com,
	hughd@...gle.com,
	william.kucharski@...cle.com,
	djwong@...nel.org,
	torvalds@...ux-foundation.org,
	ddutile@...hat.com,
	zhenyzha@...hat.com,
	shan.gavin@...il.com
Subject: [PATCH v2 2/4] mm/readahead: Limit page cache size in page_cache_ra_order()

In page_cache_ra_order(), the maximal order of the page cache to be
allocated shouldn't be larger than MAX_PAGECACHE_ORDER. Otherwise,
it's possible the large page cache can't be supported by xarray when
the corresponding xarray entry is split.

For example, HPAGE_PMD_ORDER is 13 on ARM64 when the base page size
is 64KB. The PMD-sized page cache can't be supported by xarray.

Fixes: 793917d997df ("mm/readahead: Add large folio readahead")
Cc: stable@...nel.org # v5.18+
Signed-off-by: Gavin Shan <gshan@...hat.com>
Acked-by: David Hildenbrand <david@...hat.com>
---
 mm/readahead.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index c1b23989d9ca..817b2a352d78 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -503,11 +503,11 @@ void page_cache_ra_order(struct readahead_control *ractl,
 
 	limit = min(limit, index + ra->size - 1);
 
-	if (new_order < MAX_PAGECACHE_ORDER) {
+	if (new_order < MAX_PAGECACHE_ORDER)
 		new_order += 2;
-		new_order = min_t(unsigned int, MAX_PAGECACHE_ORDER, new_order);
-		new_order = min_t(unsigned int, new_order, ilog2(ra->size));
-	}
+
+	new_order = min_t(unsigned int, MAX_PAGECACHE_ORDER, new_order);
+	new_order = min_t(unsigned int, new_order, ilog2(ra->size));
 
 	/* See comment in page_cache_ra_unbounded() */
 	nofs = memalloc_nofs_save();
-- 
2.45.1