Re: [RFC PATCH v2 2/4] mm/damon: Support for synchrounous huge pages collapse

[SeongJae Park <sj@kernel.org>]

On Tue, 10 Mar 2026 16:24:18 +0000 <gutierrez.asier@huawei-partners.com> wrote:

> From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

Please add more descriptions of the change, including the motivation.

I assume the motivation is similar to MADV_COLLAPSE that aims to make
synchronous and therefore faster huge page collapsing impacts copared to
MADV_HUGEPAGE?  It would be nice to make it clear here.  Also, if my assumption
is not wrong, adding a test results showing the benefit of DAMOS_COLLAPSE over
DAMOS_HUGEPAGE here would be nice.

> 
> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> Co-developed-by: Anatoly Stepanov <stepanov.anatoly@huawei.com>
> ---
>  include/linux/damon.h | 1 +
>  mm/damon/vaddr.c      | 3 +++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index a4fea23da857..a9cf17b9e8fa 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -142,6 +142,7 @@ enum damos_action {
>  	DAMOS_LRU_DEPRIO,
>  	DAMOS_MIGRATE_HOT,
>  	DAMOS_MIGRATE_COLD,
> +	DAMOS_COLLAPSE,
>  	DAMOS_STAT,		/* Do nothing but only record the stat */
>  	NR_DAMOS_ACTIONS,
>  };
> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> index 729b7ffd3565..36791a9a1094 100644
> --- a/mm/damon/vaddr.c
> +++ b/mm/damon/vaddr.c
> @@ -969,6 +969,9 @@ static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx,
>  	case DAMOS_NOHUGEPAGE:
>  		madv_action = MADV_NOHUGEPAGE;
>  		break;
> +	case DAMOS_COLLAPSE:
> +		madv_action = MADV_COLLAPSE;
> +		break;
>  	case DAMOS_MIGRATE_HOT:
>  	case DAMOS_MIGRATE_COLD:
>  		return damos_va_migrate(t, r, scheme, sz_filter_passed);
> -- 
> 2.43.0

The code looks good to me.


Thanks,
SJ

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