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

[Gutierrez Asier <gutierrez.asier@huawei-partners.com>]

On 3/11/2026 4:02 AM, SeongJae Park wrote:
> 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.

You are right. I will make it more clear in the cover letter for the next
version.

> 
>>
>> 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
> 
> [...]
> 

-- 
Asier Gutierrez
Huawei