[PATCH v2] swap: cond_resched in swap_cgroup_prepare()

[Yu Zhao]

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.

Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
---
Changelog since v1:
* clarify the problem in the commit message

 mm/swap_cgroup.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
index ac6318a064d3..3405b4ee1757 100644
--- 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:
-- 
2.13.0.506.g27d5fe0cd-goog