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 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> 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 (5): mm/mprotect: minor can_change_pte_writable() cleanups mm/huge_memory: try avoiding write faults when changing PMD protection 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 | 2 + include/linux/pgtable.h | 24 ------ mm/debug_vm_pgtable.c | 32 -------- mm/huge_memory.c | 66 ++++++++++++---- mm/ksm.c | 9 +-- mm/memory.c | 19 ++++- mm/mprotect.c | 33 ++++---- tools/testing/selftests/vm/anon_cow.c | 49 +++++++++++- 10 files changed, 145 insertions(+), 171 deletions(-) -- 2.38.1
