linux-kernel - Re: [RFC PATCH 0/2] Add disable_unmap

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Message-ID: <ZtBMO1owCU3XmagV@tiehlicka>
Date: Thu, 29 Aug 2024 12:23:55 +0200
From: Michal Hocko <mhocko@...e.com>
To: Zhongkun He <hezhongkun.hzk@...edance.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, roman.gushchin@...ux.dev,
	shakeel.butt@...ux.dev, muchun.song@...ux.dev,
	lizefan.x@...edance.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] Add disable_unmap_file arg to memory.reclaim

On Thu 29-08-24 18:19:16, Zhongkun He wrote:
> This patch proposes augmenting the memory.reclaim interface with a
> disable_unmap_file argument that will skip the mapped pages in
> that reclaim attempt.
> 
> For example:
> 
> echo "2M disable_unmap_file" > /sys/fs/cgroup/test/memory.reclaim
> 
> will perform reclaim on the test cgroup with no mapped file page.
> 
> The memory.reclaim is a useful interface. We can carry out proactive
> memory reclaim in the user space, which can increase the utilization
> rate of memory. 
> 
> In the actual usage scenarios, we found that when there are sufficient
> anonymous pages, mapped file pages with a relatively small proportion
> would still be reclaimed. This is likely to cause an increase in
> refaults and an increase in task delay, because mapped file pages
> usually include important executable codes, data, and shared libraries,
> etc. According to the verified situation, if we can skip this part of
> the memory, the task delay will be reduced.

Do you have examples of workloads where this is demonstrably helps and
cannot be tuned via swappiness?
-- 
Michal Hocko
SUSE Labs