linux-kernel - Re: [RFC PATCH v3 5/7] mm/damon/paddr: introduce DAMOS_MIGRATE

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Date: Tue,  9 Apr 2024 09:18:47 -0700
From: SeongJae Park <sj@...nel.org>
To: Honggyu Kim <honggyu.kim@...com>
Cc: SeongJae Park <sj@...nel.org>,
	damon@...ts.linux.dev,
	linux-mm@...ck.org,
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	art.jeongseob@...il.com
Subject: Re: [RFC PATCH v3 5/7] mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion

Hi Honggyu,

On Tue,  9 Apr 2024 18:54:14 +0900 Honggyu Kim <honggyu.kim@...com> wrote:
> On Mon,  8 Apr 2024 10:52:28 -0700 SeongJae Park <sj@...nel.org> wrote:
> > On Mon,  8 Apr 2024 21:06:44 +0900 Honggyu Kim <honggyu.kim@...com> wrote:
> > > On Fri,  5 Apr 2024 12:24:30 -0700 SeongJae Park <sj@...nel.org> wrote:
> > > > On Fri,  5 Apr 2024 15:08:54 +0900 Honggyu Kim <honggyu.kim@...com> wrote:
[...]
> > > I can remove it, but I would like to have more discussion about this
> > > issue.  The current implementation allows only a single migration
> > > target with "target_nid", but users might want to provide fall back
> > > migration target nids.
> > > 
> > > For example, if more than two CXL nodes exist in the system, users might
> > > want to migrate cold pages to any CXL nodes.  In such cases, we might
> > > have to make "target_nid" accept comma separated node IDs.  nodemask can
> > > be better but we should provide a way to change the scanning order.
> > > 
> > > I would like to hear how you think about this.
> > 
> > Good point.  I think we could later extend the sysfs file to receive the
> > comma-separated numbers, or even mask.  For simplicity, adding sysfs files
> > dedicated for the different format of inputs could also be an option (e.g.,
> > target_nids_list, target_nids_mask).  But starting from this single node as is
> > now looks ok to me.
> 
> If you think we can start from a single node, then I will keep it as is.
> But are you okay if I change the same 'target_nid' to accept
> comma-separated numbers later?  Or do you want to introduce another knob
> such as 'target_nids_list'?  What about rename 'target_nid' to
> 'target_nids' at the first place?

I have no strong concern or opinion about this at the moment.  Please feel free
to renaming it to 'taget_nids' if you think that's better.

[...]
> Please note that I will be out of office this week so won't be able to
> answer quickly.

No problem, I hope you to take and enjoy your time :)


Thanks,
SJ

[...]