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

["Yin, Fengwei" <fengwei.yin@intel.com>]

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.

Regards
Yin, Fengwei