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(-)