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

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Message-ID: <20260204002900.49291-1-sj@kernel.org>
Date: Tue,  3 Feb 2026 16:28:58 -0800
From: SeongJae Park <sj@...nel.org>
To: Ravi Jonnalagadda <ravis.opensrc@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
	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 Tue, 3 Feb 2026 11:48:06 -0800 Ravi Jonnalagadda <ravis.opensrc@...il.com> wrote:

> 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.

Sounds good!

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

Looking forward to it!


Thanks,
SJ

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