The patch titled
Subject: mm: use memalloc_nofs_save in readahead path
has been added to the -mm tree. Its filename is
mm-use-memalloc_nofs_save-in-readahead-path.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-use-memalloc_nofs_save-in-readahead-path.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-use-memalloc_nofs_save-in-readahead-path.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: mm: use memalloc_nofs_save in readahead path
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.
Link: http://lkml.kernel.org/r/20200414150233.24495-16-willy@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reported-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Chao Yu <yuchao0@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
Cc: Gao Xiang <gaoxiang25@xxxxxxxxxx>
Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
Cc: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/readahead.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
--- a/mm/readahead.c~mm-use-memalloc_nofs_save-in-readahead-path
+++ a/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"
@@ -186,6 +187,18 @@ void page_cache_readahead_unbounded(stru
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.
*/
for (i = 0; i < nr_to_read; i++) {
@@ -229,6 +242,7 @@ void page_cache_readahead_unbounded(stru
* will then handle the error.
*/
read_pages(&rac, &page_pool, false);
+ memalloc_nofs_restore(nofs);
}
EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded);
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
mm-move-readahead-prototypes-from-mmh.patch
mm-return-void-from-various-readahead-functions.patch
mm-ignore-return-value-of-readpages.patch
mm-move-readahead-nr_pages-check-into-read_pages.patch
mm-add-new-readahead_control-api.patch
mm-use-readahead_control-to-pass-arguments.patch
mm-rename-various-offset-parameters-to-index.patch
mm-rename-readahead-loop-variable-to-i.patch
mm-remove-page_offset-from-readahead-loop.patch
mm-put-readahead-pages-in-cache-earlier.patch
mm-add-readahead-address-space-operation.patch
mm-move-end_index-check-out-of-readahead-loop.patch
mm-add-page_cache_readahead_unbounded.patch
mm-document-why-we-dont-set-pagereadahead.patch
mm-use-memalloc_nofs_save-in-readahead-path.patch
fs-convert-mpage_readpages-to-mpage_readahead.patch
btrfs-convert-from-readpages-to-readahead.patch
erofs-convert-uncompressed-files-from-readpages-to-readahead.patch
erofs-convert-compressed-files-from-readpages-to-readahead.patch
ext4-convert-from-readpages-to-readahead.patch
ext4-pass-the-inode-to-ext4_mpage_readpages.patch
f2fs-convert-from-readpages-to-readahead.patch
f2fs-pass-the-inode-to-f2fs_mpage_readpages.patch
fuse-convert-from-readpages-to-readahead.patch
iomap-convert-from-readpages-to-readahead.patch
