linux-kernel - [PATCH 0/7] Optimize mprotect for large folios

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Message-Id: <20250428120414.12101-1-dev.jain@arm.com>
Date: Mon, 28 Apr 2025 17:34:07 +0530
From: Dev Jain <dev.jain@....com>
To: akpm@...ux-foundation.org
Cc: ryan.roberts@....com,
	david@...hat.com,
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	Dev Jain <dev.jain@....com>
Subject: [PATCH 0/7] Optimize mprotect for large folios

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.

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(-)

-- 
2.30.2