[PATCH v4 0/5] Speed up mremap on large regions

[Kalesh Singh]

This is a repost of the mremap speed up patches, adding Kirill's
Acked-by's (from a separate discussion). The previous versions are
posted at:
v1 - https://lore.kernel.org/r/20200930222130.4175584-1-kaleshsingh@xxxxxxxxxx
v2 - https://lore.kernel.org/r/20201002162101.665549-1-kaleshsingh@xxxxxxxxxx
v3 - http://lore.kernel.org/r/20201005154017.474722-1-kaleshsingh@xxxxxxxxxx

mremap time can be optimized by moving entries at the PMD/PUD level if
the source and destination addresses are PMD/PUD-aligned and
PMD/PUD-sized. Enable moving at the PMD and PUD levels on arm64 and
x86. Other architectures where this type of move is supported and known to
be safe can also opt-in to these optimizations by enabling HAVE_MOVE_PMD
and HAVE_MOVE_PUD.

Observed Performance Improvements for remapping a PUD-aligned 1GB-sized
region on x86 and arm64:

    - HAVE_MOVE_PMD is already enabled on x86 : N/A
    - Enabling HAVE_MOVE_PUD on x86   : ~13x speed up

    - Enabling HAVE_MOVE_PMD on arm64 : ~ 8x speed up
    - Enabling HAVE_MOVE_PUD on arm64 : ~19x speed up

          Altogether, HAVE_MOVE_PMD and HAVE_MOVE_PUD
          give a total of ~150x speed up on arm64.

Changes in v2:
  - Reduce mremap_test time by only validating a configurable
    threshold of the remapped region, as per John.
  - Use a random pattern for mremap validation. Provide pattern
    seed in test output, as per John.
  - Moved set_pud_at() to separate patch, per Kirill.
  - Use switch() instead of ifs in move_pgt_entry(), per Kirill.
  - Update commit message with description of Android
    garbage collector use case for HAVE_MOVE_PUD, as per Joel.
  - Fix build test error reported by kernel test robot in [1].

Changes in v3:
  - Make lines 80 cols or less where they don’t need to be longer,
    per John.
  - Removed unused PATTERN_SIZE in mremap_test
  - Added Reviewed-by tag for patch 1/5 (mremap kselftest patch).
  - Use switch() instead of ifs in get_extent(), per Kirill
  - Add BUILD_BUG() is get_extent() default case.
  - Move get_old_pud() and alloc_new_pud() out of
    #ifdef CONFIG_HAVE_MOVE_PUD, per Kirill.
  - Have get_old_pmd() and alloc_new_pmd() use get_old_pud() and
    alloc_old_pud(), per Kirill.
  - Replace #ifdef CONFIG_HAVE_MOVE_PMD / PUD in move_page_tables()
    with IS_ENABLED(CONFIG_HAVE_MOVE_PMD / PUD), per Kirill.
  - Fold Add set_pud_at() patch into patch 4/5, per Kirill.

[1] https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx/thread/CKPGL4FH4NG7TGH2CVYX2UX76L25BTA3/

Kalesh Singh (5):
  kselftests: vm: Add mremap tests
  arm64: mremap speedup - Enable HAVE_MOVE_PMD
  mm: Speedup mremap on 1GB or larger regions
  arm64: mremap speedup - Enable HAVE_MOVE_PUD
  x86: mremap speedup - Enable HAVE_MOVE_PUD

 arch/Kconfig                             |   7 +
 arch/arm64/Kconfig                       |   2 +
 arch/arm64/include/asm/pgtable.h         |   1 +
 arch/x86/Kconfig                         |   1 +
 mm/mremap.c                              | 230 ++++++++++++---
 tools/testing/selftests/vm/.gitignore    |   1 +
 tools/testing/selftests/vm/Makefile      |   1 +
 tools/testing/selftests/vm/mremap_test.c | 344 +++++++++++++++++++++++
 tools/testing/selftests/vm/run_vmtests   |  11 +
 9 files changed, 558 insertions(+), 40 deletions(-)
 create mode 100644 tools/testing/selftests/vm/mremap_test.c

-- 
2.28.0.1011.ga647a8990f-goog