[PATCH 14/14] skip readahead if the cgroup is congested

[Josef Bacik <josef@toxicpanda.com>]

From: Josef Bacik <jbacik@fb.com>

We noticed in testing we'd get pretty bad latency stalls under heavy
pressure because read ahead would try to do its thing while the cgroup
was under severe pressure.  If we're under this much pressure we want to
do as little IO as possible so we can still make progress on real work
if we're a throttled cgroup, so just skip readahead if our group is
under pressure.

Signed-off-by: Josef Bacik <jbacik@fb.com>
---
 mm/readahead.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/readahead.c b/mm/readahead.c
index 539bbb6c1fad..cda6b09e0a59 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -19,6 +19,7 @@
 #include <linux/syscalls.h>
 #include <linux/file.h>
 #include <linux/mm_inline.h>
+#include <linux/blk-cgroup.h>
 
 #include "internal.h"
 
@@ -500,6 +501,9 @@ void page_cache_sync_readahead(struct address_space *mapping,
 	if (!ra->ra_pages)
 		return;
 
+	if (blk_cgroup_congested())
+		return;
+
 	/* be dumb */
 	if (filp && (filp->f_mode & FMODE_RANDOM)) {
 		force_page_cache_readahead(mapping, filp, offset, req_size);
@@ -550,6 +554,9 @@ page_cache_async_readahead(struct address_space *mapping,
 	if (inode_read_congested(mapping->host))
 		return;
 
+	if (blk_cgroup_congested())
+		return;
+
 	/* do read-ahead */
 	ondemand_readahead(mapping, ra, filp, true, offset, req_size);
 }
-- 
2.14.3