Re: [PATCH v10 07/13] khugepaged: skip collapsing mTHP to smaller orders

[Dev Jain <dev.jain@arm.com>]

On 21/08/25 5:35 pm, Lorenzo Stoakes wrote:
>
>
>> ---
>>   mm/khugepaged.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index 1ad7e00d3fd6..6a4cf7e4a7cc 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -611,6 +611,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>>   		folio = page_folio(page);
>>   		VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio);
>>
>> +		/*
>> +		 * TODO: In some cases of partially-mapped folios, we'd actually
>> +		 * want to collapse.
>> +		 */
> Not a fan of adding todo's in code, they have a habit of being left forever. I'd
> maybe put a more written  out comment something similar to the commit message.

I had suggested to add in https://lore.kernel.org/all/20250211111326.14295-10-dev.jain@arm.com/
from the get go, but then we decided to leave it for later. So rest assured this TODO won't
be left forever : )

>
>> +		if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) {
>> +			result = SCAN_PTE_MAPPED_HUGEPAGE;
>> +			goto out;
>> +		}
>> +
>>   		/* See collapse_scan_pmd(). */
>>   		if (folio_maybe_mapped_shared(folio)) {
>>   			++shared;
>> --
>> 2.50.1
>>