Messages in this thread | | | From | David Hildenbrand <> | Subject | [PATCH v1 0/7] mm/ksm: break_ksm() cleanups and fixes | Date | Fri, 30 Sep 2022 16:19:24 +0200 |
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This series cleans up and fixes break_ksm(). In summary, we no longer use fake write faults to break COW but instead FAULT_FLAG_UNSHARE. Further, we move away from using follow_page() [that we can hopefully remove completely at one point] and use new walk_page_range_vma() instead.
Fortunately, we can get rid of VM_FAULT_WRITE and FOLL_MIGRATION in common code now.
Add a selftest to measure MADV_UNMERGEABLE performance. In my setup (AMD Ryzen 9 3900X), running the KSM selftest to test unmerge performance on 2 GiB (taskset 0x8 ./ksm_tests -D -s 2048), this results in a performance degradation of ~8% -- 9% (old: ~5250 MiB/s, new: ~4800 MiB/s). I don't think we particularly care for now, but it's good to be aware of the implication.
Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Shuah Khan <shuah@kernel.org> Cc: Hugh Dickins <hughd@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Peter Xu <peterx@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com>
David Hildenbrand (7): selftests/vm: add test to measure MADV_UNMERGEABLE performance mm/ksm: simplify break_ksm() to not rely on VM_FAULT_WRITE mm: remove VM_FAULT_WRITE mm/ksm: fix KSM COW breaking with userfaultfd-wp via FAULT_FLAG_UNSHARE mm/pagewalk: add walk_page_range_vma() mm/ksm: convert break_ksm() to use walk_page_range_vma() mm/gup: remove FOLL_MIGRATION
include/linux/mm.h | 1 - include/linux/mm_types.h | 3 - include/linux/pagewalk.h | 3 + mm/gup.c | 55 ++----------- mm/huge_memory.c | 2 +- mm/ksm.c | 103 +++++++++++++++++++------ mm/memory.c | 9 +-- mm/pagewalk.c | 27 +++++++ tools/testing/selftests/vm/ksm_tests.c | 76 +++++++++++++++++- 9 files changed, 192 insertions(+), 87 deletions(-)
-- 2.37.3
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