[RFC PATCH V5 0/6] get_user_pages_fast for ARM and ARM64

[Steve Capper]

Hello,
This RFC series implements get_user_pages_fast and __get_user_pages_fast.
These are required for Transparent HugePages to function correctly, as
a futex on a THP tail will otherwise result in an infinite loop (due to
the core implementation of __get_user_pages_fast always returning 0).
This series may also be beneficial for direct-IO heavy workloads and
certain KVM workloads.

The main changes since RFC V4 are:
 * corrected the arm64 logic so it now correctly rcu-frees page
   table backing pages.
 * rcu free logic relaxed for pre-ARMv7 ARM as we need an IPI to
   invalidate TLBs anyway.
 * rebased to 3.15-rc3 (some minor changes were needed to allow it to merge).
 * dropped Catalin's mmu_gather patch as that's been merged already.

I would really appreciate any comments (especially on the validity or
otherwise of the core fast_gup implementation) and/or testers.

Cheers,
--
Steve



Steve Capper (6):
  mm: Introduce a general RCU get_user_pages_fast.
  arm: mm: Introduce special ptes for LPAE
  arm: mm: Enable HAVE_RCU_TABLE_FREE logic
  arm: mm: Enable RCU fast_gup
  arm64: mm: Enable HAVE_RCU_TABLE_FREE logic
  arm64: mm: Enable RCU fast_gup

 arch/arm/Kconfig                      |   4 +
 arch/arm/include/asm/pgtable-2level.h |   2 +
 arch/arm/include/asm/pgtable-3level.h |  14 ++
 arch/arm/include/asm/pgtable.h        |   6 +-
 arch/arm/include/asm/tlb.h            |  38 ++++-
 arch/arm/mm/flush.c                   |  19 +++
 arch/arm64/Kconfig                    |   4 +
 arch/arm64/include/asm/pgtable.h      |   8 +-
 arch/arm64/include/asm/tlb.h          |  18 ++-
 arch/arm64/mm/flush.c                 |  19 +++
 mm/Kconfig                            |   3 +
 mm/Makefile                           |   1 +
 mm/gup.c                              | 297 ++++++++++++++++++++++++++++++++++
 13 files changed, 424 insertions(+), 9 deletions(-)
 create mode 100644 mm/gup.c

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1.8.1.4