linux-kernel - Re: [RFC PATCH 0/3] mm: memcontrol: delayed force empty

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Message-ID: <20190103101215.GH31793@dhcp22.suse.cz>
Date:   Thu, 3 Jan 2019 11:12:15 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     hannes@...xchg.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] mm: memcontrol: delayed force empty

On Thu 03-01-19 04:05:30, Yang Shi wrote:
> 
> Currently, force empty reclaims memory synchronously when writing to
> memory.force_empty.  It may take some time to return and the afterwards
> operations are blocked by it.  Although it can be interrupted by signal,
> it still seems suboptimal.

Why it is suboptimal? We are doing that operation on behalf of the
process requesting it. What should anybody else pay for it? In other
words why should we hide the overhead?

> Now css offline is handled by worker, and the typical usecase of force
> empty is before memcg offline.  So, handling force empty in css offline
> sounds reasonable.

Hmm, so I guess you are talking about
echo 1 > $MEMCG/force_empty
rmdir $MEMCG

and you are complaining that the operation takes too long. Right? Why do
you care actually?
-- 
Michal Hocko
SUSE Labs