Re: [RFC PATCH] mm: populate multiple PTEs if file page is large folio

[David Hildenbrand <david@redhat.com>]

On 17.01.23 10:19, Yin, Fengwei wrote:
> 
> 
> On 1/14/2023 2:13 AM, Matthew Wilcox wrote:
>> On Sat, Jan 14, 2023 at 12:35:38AM +0800, Yin Fengwei wrote:
>>> The page fault number can be reduced by batched PTEs population.
>>> The batch size of PTEs population is not allowed to cross:
>>>    - page table boundaries
>>>    - vma range
>>>    - large folio size
>>>    - fault_around_bytes
>>
>> I find this patch very interesting.  But is it really worth it?  Most
>> file-backed page faults are resolved through the ->map_pages() path
>> which is almost always filemap_map_pages(), which does something
>> fairly similar to this already.  Do you have any performance numbers?
>>
> I tried the will-it-scale page_fault3:
> https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault3.c
> with 96 processes on a test box with 48C/86T.
> 
> The test result got about 3.75X better with 4.1X less page fault number
> with this patch.
> 
> But It's a micro benchmark which shows extreme friendly case to this patch.
> 
> I didn't see observed performance gain with other workloads. I suppose
> shared file write operations may not be common operations? Thanks.

One question I have after reading "which does something fairly similar 
to this already", if both paths could be unified.

-- 
Thanks,

David / dhildenb