Re: [PATCH v4 0/4] Optimize mprotect() for large folios

[Dev Jain]

On 30/06/25 4:35 am, Andrew Morton wrote:
> On Sat, 28 Jun 2025 17:04:31 +0530 Dev Jain <dev.jain@xxxxxxx> wrote:
>
> > This patchset optimizes the mprotect() system call for large folios
> > by PTE-batching. No issues were observed with mm-selftests, build
> > tested on x86_64.
> um what.  Seems to claim that "selftests still compiles after I messed
> with stuff", which isn't very impressive ;)  Please clarify?

Sorry I mean to say that the mm-selftests pass.

> > We use the following test cases to measure performance, mprotect()'ing
> > the mapped memory to read-only then read-write 40 times:
> >
> > Test case 1: Mapping 1G of memory, touching it to get PMD-THPs, then
> > pte-mapping those THPs
> > Test case 2: Mapping 1G of memory with 64K mTHPs
> > Test case 3: Mapping 1G of memory with 4K pages
> >
> > Average execution time on arm64, Apple M3:
> > Before the patchset:
> > T1: 7.9 seconds   T2: 7.9 seconds   T3: 4.2 seconds
> >
> > After the patchset:
> > T1: 2.1 seconds   T2: 2.2 seconds   T3: 4.3 seconds
> Well that's tasty.
>
> > Observing T1/T2 and T3 before the patchset, we also remove the regression
> > introduced by ptep_get() on a contpte block. And, for large folios we get
> > an almost 74% performance improvement, albeit the trade-off being a slight
> > degradation in the small folio case.