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Message-ID: <20190130211226.GA6216@castle.DHCP.thefacebook.com>
Date: Wed, 30 Jan 2019 21:12:35 +0000
From: Roman Gushchin <guro@...com>
To: Chris Down <chris@...isdown.name>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>, Tejun Heo <tj@...nel.org>,
Dennis Zhou <dennis@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v3] mm: Make memory.emin the baseline for utilisation
determination
On Tue, Jan 29, 2019 at 02:15:25PM -0500, Chris Down wrote:
> Roman points out that when when we do the low reclaim pass, we scale the
> reclaim pressure relative to position between 0 and the maximum
> protection threshold.
>
> However, if the maximum protection is based on memory.elow, and
> memory.emin is above zero, this means we still may get binary behaviour
> on second-pass low reclaim. This is because we scale starting at 0, not
> starting at memory.emin, and since we don't scan at all below emin, we
> end up with cliff behaviour.
>
> This should be a fairly uncommon case since usually we don't go into the
> second pass, but it makes sense to scale our low reclaim pressure
> starting at emin.
>
> You can test this by catting two large sparse files, one in a cgroup
> with emin set to some moderate size compared to physical RAM, and
> another cgroup without any emin. In both cgroups, set an elow larger
> than 50% of physical RAM. The one with emin will have less page
> scanning, as reclaim pressure is lower.
>
> Signed-off-by: Chris Down <chris@...isdown.name>
> Suggested-by: Roman Gushchin <guro@...com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Roman Gushchin <guro@...com>
> Cc: Dennis Zhou <dennis@...nel.org>
> Cc: linux-kernel@...r.kernel.org
> Cc: cgroups@...r.kernel.org
> Cc: linux-mm@...ck.org
> Cc: kernel-team@...com
Acked-by: Roman Gushchin <guro@...com>
Thanks!
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