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@xxxxxxxxxxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
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
