linux-kernel - Re: [PATCH] mm/damon/vaddr: Skip isolating folios already in destination nid

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Message-Id: <20250725193952.49563-1-sj@kernel.org>
Date: Fri, 25 Jul 2025 12:39:52 -0700
From: SeongJae Park <sj@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: SeongJae Park <sj@...nel.org>,
	Bijan Tabatabai <bijan311@...il.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	damon@...ts.linux.dev,
	Bijan Tabatabai <bijantabatab@...ron.com>
Subject: Re: [PATCH] mm/damon/vaddr: Skip isolating folios already in destination nid

+ Andrew

On Fri, 25 Jul 2025 12:36:37 -0700 SeongJae Park <sj@...nel.org> wrote:

> On Fri, 25 Jul 2025 11:33:00 -0500 Bijan Tabatabai <bijan311@...il.com> wrote:
> 
> > From: Bijan Tabatabai <bijantabatab@...ron.com>
> > 
> > damos_va_migrate_dests_add() determines the node a folio should be in
> > based on the struct damos_migrate_dests associated with the migration
> > scheme and adds the folio to the linked list corresponding to that node
> > so it can be migrated later. Currently, folios are isolated and added to
> > the list even if they are already in the node they should be in.
> > 
> > In using damon weighted interleave more, I've found that the overhead of
> > needlessly adding these folios to the migration lists can be quite
> > high. The overhead comes from isolating folios and placing them in the
> > migration lists inside of damos_va_migrate_dests_add(), as well as the
> > cost of handling those folios in damon_migrate_pages(). This patch
> > eliminates that overhead by simply avoiding the addition of folios that
> > are already in their intended location to the migration list.
> [...]
> > Signed-off-by: Bijan Tabatabai <bijantabatab@...ron.com>
> 
> Reviewed-by: SeongJae Park <sj@...nel.org>
> 
> > ---
> > Sorry I missed this in the original patchset!
> 
> No worry!
> 
> Andrew, could we squash this into commit 19c1dc15c859 ("mm/damon/vaddr: use
> damos->migrate_dests in migrate_{hot,cold}") on mm-stable?  I think this is
> just a simple fixup.
> 
> > 
> >  mm/damon/vaddr.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> > index 7f5dc9c221a0..4404c2ab0583 100644
> > --- a/mm/damon/vaddr.c
> > +++ b/mm/damon/vaddr.c
> > @@ -711,6 +711,10 @@ static void damos_va_migrate_dests_add(struct folio *folio,
> >  		target -= dests->weight_arr[i];
> >  	}
> >  
> > +	/* If the folio is already in the right node, don't do anything */
> > +	if (folio_nid(folio) == dests->node_id_arr[i])
> > +		return;
> > +
> >  isolate:
> >  	if (!folio_isolate_lru(folio))
> >  		return;
> > -- 
> > 2.43.5
> 
> 
> Thanks,
> SJ
>