Re: [linux-next:master] [mm] f66e2727dd: stress-ng.rawsock.ops_per_sec 46.9% regression

[Sid Kumar <sidhartha.kumar@oracle.com>]

On 11/26/25 3:49 AM, David Hildenbrand (Red Hat) wrote:
> On 11/25/25 15:46, kernel test robot wrote:
>>
>>
>> Hello,
>>
>> kernel test robot noticed a 46.9% regression of 
>> stress-ng.rawsock.ops_per_sec on:
>>
>>
>> commit: f66e2727ddfcbbe3dbb459e809824f721a914464 ("mm: huge_memory: 
>> use folio_can_map_prot_numa() for pmd folio")
>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>
> Unexpected, but maybe simple a symptom of doing the right thing?
>
> "which skips unsuitable folio, i.e.  zone device, shared folios (KSM, 
> CoW), non-movable dma pinned, dirty file folio and folios that already 
> have the expected node affinity."
>
> I suspect skipping shared folios or dirty file folios might make the 
> difference. The benchmark results would be misleading in that case: as 
> we shouldn't have migrated these pages in the first place beforehand.


Reproducing the benchmark and adding prints to show which condition the 
return false occurs in shows that:

     /* Also skip shared copy-on-write folios */
     if (is_cow_mapping(vma->vm_flags) && 
folio_maybe_mapped_shared(folio)) {
         printk("false at is_Cow_mapping\n");
         return false;
     }

virtme-ng% dmesg | grep is_Cow_mapping | wc -l
25302

is the condition that now fails and leads to the regression.


Thanks,

Sid