linux-kernel - Re: [PATCH RFC] mm/memcontrol: reclaim severe usage over high limit in get_user

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Date:   Mon, 29 Jul 2019 20:48:50 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <shy828301@...il.com>
Cc:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        cgroups@...r.kernel.org, Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH RFC] mm/memcontrol: reclaim severe usage over high limit
 in get_user_pages loop

On Mon 29-07-19 10:28:43, Yang Shi wrote:
[...]
> I don't worry too much about scale since the scale issue is not unique
> to background reclaim, direct reclaim may run into the same problem.

Just to clarify. By scaling problem I mean 1:1 kswapd thread to memcg.
You can have thousands of memcgs and I do not think we really do want
to create one kswapd for each. Once we have a kswapd thread pool then we
get into a tricky land where a determinism/fairness would be non trivial
to achieve. Direct reclaim, on the other hand is bound by the workload
itself.
-- 
Michal Hocko
SUSE Labs