[RFC v4 00/20] Speculative page faults

[Laurent Dufour]

This is a port on kernel 4.12 of the work done by Peter Zijlstra to
handle page fault without holding the mm semaphore.

http://linux-kernel.2935.n7.nabble.com/RFC-PATCH-0-6-Another-go-at-speculative-page-faults-tt965642.html#none

Compared to the Peter initial work, this series introduce a try spin
lock when dealing with speculative page fault. This is required to
avoid dead lock when handling a page fault while a TLB invalidate is
requested by an other CPU holding the PTE. Another change due to a
lock dependency issue with mapping->i_mmap_rwsem.

This series also protect changes to VMA's data which are read or
change by the page fault handler. The protections is done through the
VMA's sequence number.

This series is functional on x86 and PowerPC.

It's building on top of v4.12-rc4 and relies on the change done by
Paul McKenney to the SRCU code allowing better performance by
maintaining per-CPU callback lists:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=da915ad5cf25b5f5d358dd3670c3378d8ae8c03e

Tests have been made using a large commercial in-memory database on a
PowerPC system with 752 CPUs. The results are very encouraging since
the loading of the 2TB database was faster by 20% with the speculative
page fault.

Since tests are encouraging and running test suite didn't raise any
issue, I'd like this request for comment series to move to a patch
series soon. So please feel free to comment.

Changes since V3:
 - support for the 5-level paging.
 - abort speculative path before entering userfault code
 - support for PowerPC architecture
 - reorder the patch to fix build test errors.

Laurent Dufour (14):
  mm: Introduce pte_spinlock
  mm/spf: Try spin lock in speculative path
  mm/spf: Fix fe.sequence init in __handle_mm_fault()
  mm/spf: don't set fault entry's fields if locking failed
  mm/spf; fix lock dependency against mapping->i_mmap_rwsem
  mm/spf: Protect changes to vm_flags
  mm/spf Protect vm_policy's changes against speculative pf
  mm/spf: Add check on the VMA's flags
  mm/spf: protect madvise vs speculative pf
  mm/spf: protect mremap() against speculative pf
  mm/spf: Don't call user fault callback in the speculative path
  x86/mm: Update the handle_speculative_fault's path
  powerpc/mm: Add speculative page fault
  mm/spf: Clear FAULT_FLAG_KILLABLE in the speculative path

Peter Zijlstra (6):
  mm: Dont assume page-table invariance during faults
  mm: Prepare for FAULT_FLAG_SPECULATIVE
  mm: VMA sequence count
  mm: RCU free VMAs
  mm: Provide speculative fault infrastructure
  x86/mm: Add speculative pagefault handling

 arch/powerpc/mm/fault.c  |  25 +++-
 arch/x86/mm/fault.c      |  14 +++
 fs/proc/task_mmu.c       |   2 +
 include/linux/mm.h       |   4 +
 include/linux/mm_types.h |   3 +
 kernel/fork.c            |   1 +
 mm/init-mm.c             |   1 +
 mm/internal.h            |  20 ++++
 mm/madvise.c             |   4 +
 mm/memory.c              | 291 +++++++++++++++++++++++++++++++++++++++--------
 mm/mempolicy.c           |  10 +-
 mm/mlock.c               |   9 +-
 mm/mmap.c                | 123 +++++++++++++++-----
 mm/mprotect.c            |   2 +
 mm/mremap.c              |   7 ++
 15 files changed, 435 insertions(+), 81 deletions(-)

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2.7.4