This series is based on mm-unstable.
As discussed in my talk at LPC, we can reuse the same mechanism for
deciding whether to map a pte writable when upgrading permissions via
mprotect() -- e.g., PROT_READ -> PROT_READ|PROT_WRITE -- to replace the
savedwrite infrastructure used for NUMA hinting faults (e.g., PROT_NONE
-> PROT_READ|PROT_WRITE).
Instead of maintaining previous write permissions for a pte/pmd, we
re-determine if the pte/pmd can be writable. The big benefit is that we
have a common logic for deciding whether we can map a pte/pmd writable on
protection changes.
For private mappings, there should be no difference -- from
what I understand, that is what autonuma benchmarks care about.
I ran autonumabench for v1 on a system with 2 NUMA nodes, 96 GiB each via:
perf stat --null --repeat 10
The numa01 benchmark is quite noisy in my environment and I failed to
reduce the noise so far.
numa01:
mm-unstable: 146.88 +- 6.54 seconds time elapsed ( +- 4.45% )
mm-unstable++: 147.45 +- 13.39 seconds time elapsed ( +- 9.08% )
numa02:
mm-unstable: 16.0300 +- 0.0624 seconds time elapsed ( +- 0.39% )
mm-unstable++: 16.1281 +- 0.0945 seconds time elapsed ( +- 0.59% )
It is worth noting that for shared writable mappings that require
writenotify, we will only avoid write faults if the pte/pmd is dirty
(inherited from the older mprotect logic). If we ever care about optimizing
that further, we'd need a different mechanism to identify whether the FS
still needs to get notified on the next write access.
In any case, such an optimiztion will then not be autonuma-specific,
but mprotect() permission upgrades would similarly benefit from it.
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
v1 -> v2:
* "mm/mprotect: factor out check whether manual PTE write upgrades are
required"
-> Added
* "mm/autonuma: use can_change_(pte|pmd)_writable() to replace savedwrite"
-> Simplify and don't opimize for failed migration
-> Update patch description
RFC -> v1:
* "mm/mprotect: allow clean exclusive anon pages to be writable"
-> Move comment change to patch #2
* "mm/mprotect: minor can_change_pte_writable() cleanups"
-> Adjust comments
* "mm/huge_memory: try avoiding write faults when changing PMD protection"
-> Fix wrong check
* "selftests/vm: anon_cow: add mprotect() optimiation tests"
-> Add basic tests for the mprotect() optimization
David Hildenbrand (6):
mm/mprotect: minor can_change_pte_writable() cleanups
mm/huge_memory: try avoiding write faults when changing PMD protection
mm/mprotect: factor out check whether manual PTE write upgrades are
required
mm/autonuma: use can_change_(pte|pmd)_writable() to replace savedwrite
mm: remove unused savedwrite infrastructure
selftests/vm: anon_cow: add mprotect() optimization tests
Nadav Amit (1):
mm/mprotect: allow clean exclusive anon pages to be writable
arch/powerpc/include/asm/book3s/64/pgtable.h | 80 +-------------------
arch/powerpc/kvm/book3s_hv_rm_mmu.c | 2 +-
include/linux/mm.h | 18 ++++-
include/linux/pgtable.h | 24 ------
mm/debug_vm_pgtable.c | 32 --------
mm/huge_memory.c | 64 ++++++++++++----
mm/ksm.c | 9 +--
mm/memory.c | 16 +++-
mm/mprotect.c | 50 ++++++------
tools/testing/selftests/vm/anon_cow.c | 49 +++++++++++-
10 files changed, 158 insertions(+), 186 deletions(-)
--
2.38.1
