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.

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@vger.kernel.org>	[5.18+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/readahead.c b/mm/readahead.c
index c1b2398..817b2a3 100644 (file)
--- 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();