Re: [PATCH mm-unstable v17 02/14] mm/khugepaged: generalize alloc_charge_folio()

[Lance Yang <lance.yang@linux.dev>]

On 2026/5/18 19:55, Usama Arif wrote:
[...]
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index 979885694351..f0e29d5c7b1f 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -1068,21 +1068,26 @@ static enum scan_result __collapse_huge_page_swapin(struct mm_struct *mm,
>>   }
>>   
>>   static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
>> -		struct collapse_control *cc)
>> +		struct collapse_control *cc, unsigned int order)
>>   {
>>   	gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
>>   		     GFP_TRANSHUGE);
>>   	int node = collapse_find_target_node(cc);
>>   	struct folio *folio;
>>   
>> -	folio = __folio_alloc(gfp, HPAGE_PMD_ORDER, node, &cc->alloc_nmask);
>> +	folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask);
>>   	if (!folio) {
>>   		*foliop = NULL;
>> -		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
>> +		if (is_pmd_order(order))
>> +			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
>> +		count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC_FAILED);
>>   		return SCAN_ALLOC_HUGE_PAGE_FAIL;
>>   	}
>>   
>> -	count_vm_event(THP_COLLAPSE_ALLOC);
>> +	if (is_pmd_order(order))
>> +		count_vm_event(THP_COLLAPSE_ALLOC);
>> +	count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC);
>> +
> 
> The vmstat THP_COLLAPSE_ALLOC counter is pmd order only.
> But after this we have
> 
> 	count_memcg_folio_events(folio, THP_COLLAPSE_ALLOC, 1);
> 
> which is not being guarded with is_pmd_order().

Good catch!

> 
> I think we want this to be pmd order only as well so that
> the meaning of the vmstat and cgroup counter remains the same?

Agreed. THP_COLLAPSE_ALLOC should remain PMD order only for
vmstat and memcg events.

So this should be guarded with is_pmd_order() as well :)

Cheers, Lance