Re: [PATCH next v2 0/2] THP COW support for private executable file mmap
From: David Hildenbrand (Red Hat)
Date: Tue Dec 30 2025 - 16:42:42 EST
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