Re: [PATCH next v2 0/2] THP COW support for private executable file mmap

["David Hildenbrand (Red Hat)" <david@kernel.org>]

On 12/28/25 04:42, Matthew Wilcox wrote:
> On Fri, Dec 26, 2025 at 06:03:35PM +0800, Zhang Qilong wrote:
>> The MySQL (Ver 8.0.25) test results on AMD are as follows:
>>
>> -------------------------------------------------------------------
>>                   | Exec mmap Rss(kB)  | Measured tpmC (NewOrders) |
>> -----------------|--------------------|---------------------------|
>>   base(page COW)  |       32868        |        339686             |
>> -----------------|--------------------|---------------------------|
>>   exec THP COW    |       43516        |        371324             |
>> -------------------------------------------------------------------
>>
>> The MySQL using exec THP COW consumes an additional 10648 kB of memory
>> but achieves 9.3% performance improvement in the scenario of hotpatch.
>> Additionally, another our internal program achieves approximately a 5%
>> performance improvement as well.
>>
>> As result, using exec THP COW will consume additional memory. The
>> additional memory consumption may be negligible for the current system.
>> It's necessary to balance the memory consumption with the performance
>> impact.
> 
> I mean ... you say "negligible", I saay "32% extra".  9% performance
> gain is certainly nothing to sneer at (and is consistent with measured
> performance gains from using large folios for, eg, kernel compiles).
> But wow, that's a lot of extra memory.  My feeling is that we shouldn't
> add this functionality, but I'd welcome other opinions.

Also, I wonder whether there aren't other approaches for such code 
patching where user space is able to create THPs more effectively? 
Handling creation of a patched file version etc in user space.

E.g., I'd assume that a single "patched" version (with a single THP) for 
multiple program instances could be beneficial over one patched version 
per program instance.

Which type of code patching does hotpatch perform?

-- 
Cheers

David