linux-kernel - Re: [RFC PATCH v0 0/2] Batch migration for NUMA balancing

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Message-Id: <20250522185219.57843-1-sj@kernel.org>
Date: Thu, 22 May 2025 11:52:19 -0700
From: SeongJae Park <sj@...nel.org>
To: Gregory Price <gourry@...rry.net>
Cc: SeongJae Park <sj@...nel.org>,
	Bharata B Rao <bharata@....com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
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Subject: Re: [RFC PATCH v0 0/2] Batch migration for NUMA balancing

On Thu, 22 May 2025 13:40:59 -0400 Gregory Price <gourry@...rry.net> wrote:

> On Thu, May 22, 2025 at 09:30:23AM -0700, SeongJae Park wrote:
> > On Wed, 21 May 2025 23:08:16 -0400 Gregory Price <gourry@...rry.net> wrote:
> > 
> > > 
> > > It seems to me that DAMON might make use of the batch migration
> > > interface, so if you need any changes or extensions, it might be good
> > > for you (SJ) to take a look at that for us.
> > 
> > For batch migration interface, though, to be honest I don't find very clear
> > DAMON's usage of it, since DAMON does region-based sort of batched migration.
> > Again, I took only a glance on migration batching part and gonna take more time
> > to the details.
> > 
> 
> DAMON would identify a set of PFNs or Folios to migrate, at some point,
> wouldn't it be beneficial to DAMON to simply re-use:
> 
> int migrate_misplaced_folio_batch(struct list_head *folio_list, int node)

Good idea.  Actually we implemnted DAMOS_MIGRATE_HOT and DAMOS_MIGRATE_COLD
instead of DAMOS_PROMOTE and DAMOS_DEMOTE since we didn't sure the promotion
path logic is somewhat everyone agreed upon.  FYI, I'm planning to revisit the
promotion path logic later (don't wait for me though ;) ).

> 
> If not, then why?

I'll need to look into the detail, but from a high level glance I think it is a
good idea.

> 
> That's why I mean by what would DAMON want out of such an interface.
> Not the async part, but the underlying migration functions.

Makes sense, thank you!


Thanks,
SJ

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