swap: cond_resched in swap_cgroup_prepare()

I saw need_resched() warnings when swapping on large swapfile (TBs)
because continuously allocating many pages in swap_cgroup_prepare() took
too long.

We already cond_resched when freeing page in swap_cgroup_swapoff().  Do
the same for the page allocation.

Link: http://lkml.kernel.org/r/20170604200109.17606-1-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
index ac6318a064d35e6dcc5385d1dc8062ff6e46554c..3405b4ee1757e3deb196c93e49b9641dad8d56fb 100644 (file)
--- a/mm/swap_cgroup.c
+++ b/mm/swap_cgroup.c
@@ -48,6 +48,9 @@ static int swap_cgroup_prepare(int type)
                if (!page)
                        goto not_enough_page;
                ctrl->map[idx] = page;
+
+               if (!(idx % SWAP_CLUSTER_MAX))
+                       cond_resched();
        }
        return 0;
 not_enough_page: