+ mm-readahead-limit-page-cache-size-in-page_cache_ra_order.patch added to mm-hotfixes-unstable branch

+ mm-readahead-limit-page-cache-size-in-page_cache_ra_order.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/readahead: limit page cache size in page_cache_ra_order()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-readahead-limit-page-cache-size-in-page_cache_ra_order.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-readahead-limit-page-cache-size-in-page_cache_ra_order.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Gavin Shan <gshan@redhat.com>
Subject: mm/readahead: limit page cache size in page_cache_ra_order()
Date: Thu, 27 Jun 2024 10:39:50 +1000

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.

Link: https://lkml.kernel.org/r/20240627003953.1262512-3-gshan@redhat.com
Fixes: 793917d997df ("mm/readahead: Add large folio readahead")
Signed-off-by: Gavin Shan <gshan@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Zhenyu Zhang <zhenyzha@redhat.com>
Cc: <stable@kernel.org>	[5.18+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/readahead.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/mm/readahead.c~mm-readahead-limit-page-cache-size-in-page_cache_ra_order
+++ a/mm/readahead.c
@@ -503,11 +503,11 @@ void page_cache_ra_order(struct readahea
 
 	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();
_

Patches currently in -mm which might be from gshan@redhat.com are

mm-filemap-make-max_pagecache_order-acceptable-to-xarray.patch
mm-readahead-limit-page-cache-size-in-page_cache_ra_order.patch
mm-filemap-skip-to-create-pmd-sized-page-cache-if-needed.patch
mm-shmem-disable-pmd-sized-page-cache-if-needed.patch