[PATCH 0/7] Optimize mprotect for large folios

[Dev Jain]

On 28/04/25 5:34 pm, 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 276% performance improvement.

Messed up the denominator, I mean ((7.9 - 2.1) / 7.9) * 100 = 73%.

> 
> 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                    | 163 +++++++++++++++++++++----------
>   mm/pgtable-generic.c             |  16 ++-
>   9 files changed, 198 insertions(+), 70 deletions(-)
>