mm: skip readahead if the cgroup is congested

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>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/mm/readahead.c b/mm/readahead.c
index e273f0de337699f8222ab6b73b126435fb6061ee..9f62b71511001a06e80db37296e3b3709c894f04 100644 (file)
--- 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"
 
@@ -505,6 +506,9 @@ 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);
@@ -555,6 +559,9 @@ 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);
 }