linux-kernel - Re: [RFC PATCH v2 0/3] mm/damon: Introduce node_target_mem

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Message-ID: <CALa+Y1475VSnrNTn-AQtTTnye+sdAGu9sVO0YMEtLidNW53_=A@mail.gmail.com>
Date: Tue, 3 Feb 2026 11:48:06 -0800
From: Ravi Jonnalagadda <ravis.opensrc@...il.com>
To: SeongJae Park <sj@...nel.org>
Cc: damon@...ts.linux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, akpm@...ux-foundation.org, corbet@....net, 
	bijan311@...il.com, ajayjoshi@...ron.com, honggyu.kim@...com, 
	yunjeong.mun@...com
Subject: Re: [RFC PATCH v2 0/3] mm/damon: Introduce node_target_mem_bp Quota
 Goal Metric

On Sat, Jan 31, 2026 at 11:54 AM SeongJae Park <sj@...nel.org> wrote:
>
> On Thu, 29 Jan 2026 17:48:06 -0800 SeongJae Park <sj@...nel.org> wrote:
>
> > On Thu, 29 Jan 2026 13:58:11 -0800 Ravi Jonnalagadda <ravis.opensrc@...il.com> wrote:
> >
> > > This series introduces a new DAMON quota goal metric, `node_target_mem_bp`,
> > > designed for controlling memory migration in heterogeneous memory systems
> > > (e.g., DRAM and CXL memory tiering).
> > >
> > > v1: https://lore.kernel.org/linux-mm/20260123045733.6954-1-ravis.opensrc@gmail.com/T/#u
> [...]
> >     Context 0: monitors node 0, migrate_hot -> node 1
> >       goal: node_ineligible_mem_bp, nid=0, target=4000
> >
> >     Context 1: monitors node 1, migrate_hot -> node 0
> >       goal: node_target_mem_bp, nid=0, target=6000
>
> In offline, Ravi enlightened me that using a single context with two schemes
> instead of the above two contexts setup can be more efficienct and useful.  I
> agree that.  It will be able to only single kdamond, and there could be more
> flexible use cases that can use the whole-memory access pattern.
>
> That is, we can use single context with the two schemes, but adding a core
> layer DAMOS filters for applying the schemes to only memory of node 0 and node
> 1, respectively.  Similar for memory tiering use cases.
>
> But I was recommending the multi contexts approach to people because the
> current implementation of DAMOS is not efficient when both quota and core layer
> filters are used.  I was actually working on making it improved, and just
> posted an RFC patch series [1].  After the patches are merged, hopefully the
> single context approach will be useful and effcient enough for varying use
> cases including the memory tiering.
>
> [1] https://lore.kernel.org/20260131194145.66286-1-sj@kernel.org
>
Thanks for providing the DAMOS_FILTER patch update SJ.

For v3, I plan to introduce two complementary metrics:
DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP
and DAMOS_QUOTA_NODE_INELIGIBLE_MEM_BP.

This will support the following approaches for hot memory migration:
1. Single context with two schemes using both metrics.
(along with DAMOS_FILTER_TYPE_ADDR)
2. Two DAMON contexts each using
DAMOS_QUOTA_NODE_INELIGIBLE_MEM_BP.

Will provide more details on the implementation and usage in the v3 series.

Thanks,
Ravi.
>
> Thanks,
> SJ
>
> [...]