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

[Matthew Wilcox]

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.