Date: Fri, 2 Jun 2017 10:18:57 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Yu Zhao <yuzhao@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>, cgroups@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] swap: cond_resched in swap_cgroup_prepare()
Message-ID: <20170602081855.GE29840@dhcp22.suse.cz>
References: <20170601195635.20744-1-yuzhao@google.com>
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On Thu 01-06-17 12:56:35, Yu Zhao wrote:
> Saw need_resched() warnings when swapping on large swapfile (TBs)
> because page allocation in swap_cgroup_prepare() took too long.

Hmm, but the page allocator makes sure to cond_resched for sleeping
allocations. I guess what you mean is something different. It is not the
allocation which took too look but there are too many of them and none
of them sleeps because there is enough memory and the allocator doesn't
sleep in that case. Right?

> We already cond_resched when freeing page in swap_cgroup_swapoff().
> Do the same for the page allocation.
> 
> Signed-off-by: Yu Zhao <yuzhao@google.com>

The patch itself makes sense to me, the changelog could see some
clarification but other than that
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  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:
> -- 
> 2.13.0.219.gdb65acc882-goog

-- 
Michal Hocko
SUSE Labs