[patch added to 3.12-stable] fs, seq_file: fallback to vmalloc instead of oom kill processes

[Jiri Slaby <jslaby@suse.cz>]

From: David Rientjes <rientjes@google.com>

This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.

===============

commit 5cec38ac866bfb8775638e71a86e4d8cac30caae upstream.

Since commit 058504edd026 ("fs/seq_file: fallback to vmalloc allocation"),
seq_buf_alloc() falls back to vmalloc() when the kmalloc() for contiguous
memory fails.  This was done to address order-4 slab allocations for
reading /proc/stat on large machines and noticed because
PAGE_ALLOC_COSTLY_ORDER < 4, so there is no infinite loop in the page
allocator when allocating new slab for such high-order allocations.

Contiguous memory isn't necessary for caller of seq_buf_alloc(), however.
Other GFP_KERNEL high-order allocations that are <=
PAGE_ALLOC_COSTLY_ORDER will simply loop forever in the page allocator and
oom kill processes as a result.

We don't want to kill processes so that we can allocate contiguous memory
in situations when contiguous memory isn't necessary.

This patch does the kmalloc() allocation with __GFP_NORETRY for high-order
allocations.  This still utilizes memory compaction and direct reclaim in
the allocation path, the only difference is that it will fail immediately
instead of oom kill processes when out of memory.

[akpm@linux-foundation.org: add comment]
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 fs/seq_file.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 6e050e26af43..96ae14abce98 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -36,7 +36,11 @@ static void *seq_buf_alloc(unsigned long size)
 {
 	void *buf;
 
-	buf = kmalloc(size, GFP_KERNEL | __GFP_NOWARN);
+	/*
+	 * __GFP_NORETRY to avoid oom-killings with high-order allocations -
+	 * it's better to fall back to vmalloc() than to kill things.
+	 */
+	buf = kmalloc(size, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
 	if (!buf && size > PAGE_SIZE)
 		buf = vmalloc(size);
 	return buf;
-- 
2.8.1