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Date:   Sun,  4 Jun 2017 13:01:09 -0700
From:   Yu Zhao <>
To:     Johannes Weiner <>,
        Michal Hocko <>,
        Vladimir Davydov <>
Cc:,,, Yu Zhao <>
Subject: [PATCH v2] swap: cond_resched in swap_cgroup_prepare()

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 <>
Acked-by: Michal Hocko <>
Acked-by: Vladimir Davydov <>
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;

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