linux-kernel - Re: [PATCH] mm: vmscan: memcg: Add global shrink priority

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Message-ID: <20191219112618.GA72828@chrisdown.name>
Date:   Thu, 19 Dec 2019 11:26:18 +0000
From:   Chris Down <chris@...isdown.name>
To:     teawater <teawaterz@...ux.alibaba.com>
Cc:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, guro@...com, shakeelb@...gle.com,
        Yang Shi <yang.shi@...ux.alibaba.com>, tj@...nel.org,
        tglx@...utronix.de, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: vmscan: memcg: Add global shrink priority

Hi Hui,

teawater writes:
>Memory.min, low, high can affect the global shrink behavior.  They can help 
>task keep some pages to help protect performance.
>
>But what I want is the low priority tasks (the tasks that performance is not 
>very important) do more shrink first.  And when low priority tasks doesn’t 
>have enough pages to be dropped and system need more free page, shrink the 
>high priority task’s pages.  Because at this time, system’s stable is more 
>important than the performance of priority task.
>With memory.min and memory.low, I have no idea to config them to support this.  
>That is why I add global shrink priority.

For sure, that's what I'm suggesting you use memory.{min,low} for -- you define 
some subset of the cgroup hierarchy as "protected", and then you bias reclaim 
away from protected cgroups (and thus *towards* unprotected cgroups) by biasing 
the size of LRU scanning. See my patch that went into 5.4 and the examples in 
the commit message:

     commit 9783aa9917f8ae24759e67bf882f1aba32fe4ea1
     Author: Chris Down <chris@...isdown.name>
     Date:   Sun Oct 6 17:58:32 2019 -0700

         mm, memcg: proportional memory.{low,min} reclaim

You can see how we're using memory.{low,min} to achieve this in this case 
study[0]. It's not exactly equivalent technically to your solution, but the end 
goals are similar.

Thanks,

Chris

0: https://facebookmicrosites.github.io/cgroup2/docs/overview.html#case-study-the-fbtax2-project