Re: [PATCH v2 0/7] Optimize mprotect for large folios

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

-cc namit@vmware.com

Also,

On future respins can we please drop Namit from vmware from cc list?

I am being spammed with these messages whenever I reply here:

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Or ask him to fix this :)

Cheers, Lorenzo

On Tue, Apr 29, 2025 at 10:53:29AM +0530, Dev Jain wrote:
> This patchset optimizes the mprotect() system call for large folios
> by PTE-batching.
>
> 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: 4.2 seconds
>
> 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.
>
> v1->v2:
>  - Rebase onto mm-unstable (6ebffe676fcf: util_macros.h: make the header more resilient)
>  - Abridge the anon-exclusive condition (Lance Yang)
>
> Dev Jain (7):
>   mm: Refactor code in mprotect
>   mm: Optimize mprotect() by batch-skipping PTEs
>   mm: Add batched versions of ptep_modify_prot_start/commit
>   arm64: Add batched version of ptep_modify_prot_start
>   arm64: Add batched version of ptep_modify_prot_commit
>   mm: Batch around can_change_pte_writable()
>   mm: Optimize mprotect() through PTE-batching
>
>  arch/arm64/include/asm/pgtable.h |  10 ++
>  arch/arm64/mm/mmu.c              |  21 +++-
>  include/linux/mm.h               |   4 +-
>  include/linux/pgtable.h          |  42 ++++++++
>  mm/gup.c                         |   2 +-
>  mm/huge_memory.c                 |   4 +-
>  mm/memory.c                      |   6 +-
>  mm/mprotect.c                    | 165 ++++++++++++++++++++-----------
>  mm/pgtable-generic.c             |  16 ++-
>  9 files changed, 198 insertions(+), 72 deletions(-)
>
> --
> 2.30.2
>