From: Johannes Weiner <hannes@cmpxchg.org>
To: Chris Down <chris@chrisdown.name>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>, Tejun Heo <tj@kernel.org>,
Roman Gushchin <guro@fb.com>, Dennis Zhou <dennis@kernel.org>,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
linux-mm@kvack.org, kernel-team@fb.com
Subject: Re: [PATCH v4] mm: Make memory.emin the baseline for utilisation determination
Date: Wed, 6 Feb 2019 15:31:17 +0100 [thread overview]
Message-ID: <20190206143117.GA30357@cmpxchg.org> (raw)
In-Reply-To: <20190201051810.GA18895@chrisdown.name>
On Fri, Feb 01, 2019 at 12:18:10AM -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@chrisdown.name>
> Suggested-by: Roman Gushchin <guro@fb.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Roman Gushchin <guro@fb.com>
> Cc: Dennis Zhou <dennis@kernel.org>
> Cc: linux-kernel@vger.kernel.org
> Cc: cgroups@vger.kernel.org
> Cc: linux-mm@kvack.org
> Cc: kernel-team@fb.com
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
prev parent reply other threads:[~2019-02-06 14:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-29 18:25 [PATCH] mm: Make memory.emin the baseline for utilisation determination Chris Down
2019-01-29 19:02 ` [PATCH v2] " Chris Down
2019-01-29 19:15 ` [PATCH v3] " Chris Down
2019-01-30 21:12 ` Roman Gushchin
2019-02-01 5:18 ` [PATCH v4] " Chris Down
2019-02-06 14:31 ` Johannes Weiner [this message]
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