Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 29 Jul 2019 20:48:50 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Yang Shi <shy828301@gmail.com>
Cc:     Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        cgroups@vger.kernel.org, Vladimir Davydov <vdavydov.dev@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH RFC] mm/memcontrol: reclaim severe usage over high limit
 in get_user_pages loop
Message-ID: <20190729184850.GH9330@dhcp22.suse.cz>
References: <156431697805.3170.6377599347542228221.stgit@buzz>
 <20190729091738.GF9330@dhcp22.suse.cz>
 <3d6fc779-2081-ba4b-22cf-be701d617bb4@yandex-team.ru>
 <20190729103307.GG9330@dhcp22.suse.cz>
 <CAHbLzkrdj-O2uXwM8ujm90OcgjyR4nAiEbFtRGe7SOoY_fs=BA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHbLzkrdj-O2uXwM8ujm90OcgjyR4nAiEbFtRGe7SOoY_fs=BA@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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