linux-kernel - Re: [PATCH -mm] vmscan: fix sane_reclaim helper for legacy memcg

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Date:	Fri, 18 Sep 2015 11:59:19 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] vmscan: fix sane_reclaim helper for legacy memcg

Hello,

On Fri, Sep 18, 2015 at 03:48:00PM +0300, Vladimir Davydov wrote:
> The sane_reclaim() helper is supposed to return false for memcg reclaim
> if the legacy hierarchy is used, because the latter lacks dirty
> throttling mechanism, and so it did before it was accidentally broken by
> commit 33398cf2f360c ("memcg: export struct mem_cgroup"). Fix it.
> 
> Fixes: 33398cf2f360c ("memcg: export struct mem_cgroup")
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index db5339dd4a32..dbc3b3ae48de 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -175,7 +175,7 @@ static bool sane_reclaim(struct scan_control *sc)
>  	if (!memcg)
>  		return true;
>  #ifdef CONFIG_CGROUP_WRITEBACK
> -	if (memcg->css.cgroup)
> +	if (cgroup_on_dfl(memcg->css.cgroup))

Just a heads-up.  I'm applying a patch which replaces cgroup_on_dfl()
with cgroup_subsys_on_dfl() to cgroup/for-4.4, so this patch would
need to be adjusted to do cgroup_subsys_on_dfl(memory_cgrp_subsys)
instead.

Thanks.

-- 
tejun
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