linux-kernel - Re: [RFC PATCH v1 1/3] mm/damon: Rebase damos watermarks for NUMA systems

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Date:   Wed, 23 Feb 2022 16:10:44 +0900
From:   Jonghyeon Kim <tome01@...u.ac.kr>
To:     SeongJae Park <sj@...nel.org>
Cc:     Jonghyeon Kim <tome01@...u.ac.kr>, Jonathan.Cameron@...wei.com,
        amit@...nel.org, benh@...nel.crashing.org, corbet@....net,
        david@...hat.com, dwmw@...zon.com, elver@...gle.com,
        foersleo@...zon.de, gthelen@...gle.com, markubo@...zon.de,
        rientjes@...gle.com, shakeelb@...gle.com, shuah@...nel.org,
        linux-damon@...zon.com, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 1/3] mm/damon: Rebase damos watermarks for NUMA
 systems

On Wed, Feb 23, 2022 at 02:10:56PM +0900, Jonghyeon Kim wrote:
> On Tue, Feb 22, 2022 at 09:53:17AM +0000, SeongJae Park wrote:
> > Hello Jonghyeon,
> > 
> 
> Hello SeongJae,
> 
> > On Fri, 18 Feb 2022 19:26:09 +0900 Jonghyeon Kim <tome01@...u.ac.kr> wrote:
> > 
> > > For NUMA systems, there is a need to allow damos to select watermark
> > > options for monitoring each NUMA node or whole system free memory. Even
> > > if we do not use NUMA, since the default NUMA node number is 0, we can
> > > monitor the whole system memory without any configuration.
> > 
> > Some users using NUMA machines but don't do NUMA-specific memory allocations
> > and therefore assume memory free rate in each NUMA node will be similar might
> > want to monitor only global free memory ratio, to limit number of kdamonds for
> > reducing CPU overhead.  In the case, this patch would make them monitor only
> > the first node.
> 
> I think that the purpose of DAMON_RECALIM is proactively reclaiming memory
> before waking up kswapd. But I missed that case you mentioned. In that case,
> they might not want to monitor each NUMA node. I agree with this.
> 
> > 
> > How about leaving DAMOS_WMARK_FREE_MEM_RATE to work as is, and adding a new
> > metric type, say, DAMOS_WMARK_NODE_FREE_MEM_RATE?
> > 
> 
> Yes, it looks good to me.
> 
> 
> Thanks,
> Jonghyeon