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

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Message-Id: <20250725193637.49389-1-sj@kernel.org>
Date: Fri, 25 Jul 2025 12:36:37 -0700
From: SeongJae Park <sj@...nel.org>
To: Bijan Tabatabai <bijan311@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	damon@...ts.linux.dev,
	akpm@...ux-foundation.org,
	Bijan Tabatabai <bijantabatab@...ron.com>
Subject: Re: [PATCH] mm/damon/vaddr: Skip isolating folios already in destination nid

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