diff mbox series

[v10,15/25] mm: Use memalloc_nofs_save in readahead path

Message ID 20200323202259.13363-16-willy@infradead.org (mailing list archive)
State New, archived
Headers show
Series Change readahead API | expand

Commit Message

Matthew Wilcox March 23, 2020, 8:22 p.m. UTC
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Ensure that memory allocations in the readahead path do not attempt to
reclaim file-backed pages, which could lead to a deadlock.  It is
possible, though unlikely this is the root cause of a problem observed
by Cong Wang.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reported-by: Cong Wang <xiyou.wangcong@gmail.com>
Suggested-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
 mm/readahead.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
diff mbox series


diff --git a/mm/readahead.c b/mm/readahead.c
index 73cb59ed5cff..3c9a8dd7c56c 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -22,6 +22,7 @@ 
 #include <linux/mm_inline.h>
 #include <linux/blk-cgroup.h>
 #include <linux/fadvise.h>
+#include <linux/sched/mm.h>
 #include "internal.h"
@@ -185,6 +186,18 @@  void page_cache_readahead_unbounded(struct address_space *mapping,
 	unsigned long i;
+	/*
+	 * Partway through the readahead operation, we will have added
+	 * locked pages to the page cache, but will not yet have submitted
+	 * them for I/O.  Adding another page may need to allocate memory,
+	 * which can trigger memory reclaim.  Telling the VM we're in
+	 * the middle of a filesystem operation will cause it to not
+	 * touch file-backed pages, preventing a deadlock.  Most (all?)
+	 * filesystems already specify __GFP_NOFS in their mapping's
+	 * gfp_mask, but let's be explicit here.
+	 */
+	unsigned int nofs = memalloc_nofs_save();
 	 * Preallocate as many pages as we will need.
@@ -229,6 +242,7 @@  void page_cache_readahead_unbounded(struct address_space *mapping,
 	 * will then handle the error.
 	read_pages(&rac, &page_pool, false);
+	memalloc_nofs_restore(nofs);