From mboxrd@z Thu Jan  1 00:00:00 1970
From: Vladimir Davydov <vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH] swap: cond_resched in swap_cgroup_prepare()
Date: Sat, 3 Jun 2017 17:58:26 +0300
Message-ID: <20170603145826.GA15130@esperanza>
References: <20170601195635.20744-1-yuzhao@google.com>
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To: Yu Zhao <yuzhao-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

On Thu, Jun 01, 2017 at 12:56:35PM -0700, Yu Zhao wrote:
> Saw need_resched() warnings when swapping on large swapfile (TBs)
> because page allocation 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-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

Acked-by: Vladimir Davydov <vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

> ---
>  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:

We should probably do the same on the error path.