From: Nadav Amit <namit@xxxxxxxxxx> This patch-set introduces access/write hints for userfaultfd. Unlike the previous versions, the use of these hints in this version is limited. Yet, in order to keep introducing new features again and again, hints are introduced for all of uffd related ioctls. The access-hint is currently used to set the young bit, similarly to do_set_pte(). This has no effect on x86, but may on arm64. When a write-hint is provided on zeropage ioctl, a clear page is allocated instead of mapping the zero-page. Future patches would use the write-hint to decide whether to map the writable pages on write-(un)protect ioctl. Setting the access-bit and dirty-bit introduces a tradeoff. When the bit is set access/write is faster, but memory reclamation might be slower. Currently, in the common userfaultfd cases the access-bit is not set on and the dirty-bit is set. This is a questionable behavior. Allow userspace to control this behavior through hints access- and write-likely hints. These hints are used to control access- and dirty-bits. For zero-pages that with write-likely hint, allocate a clear page instead of mapping the zero-page. v1 -> v2: * Leave dirty-bit as it was before [Peter Xu] RFCv2 -> v1: * Adding hints to zeropage and continue * Fixing other issues pointed by David H. & Peter Xu * Adding tests to ./run_vmtests.sh Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx> Nadav Amit (5): userfaultfd: introduce uffd_flags userfaultfd: introduce access-likely mode for common operations userfaultfd: introduce write-likely mode for uffd operations userfaultfd: zero access/write hints selftest/userfaultfd: test read/write hints fs/userfaultfd.c | 77 ++++++++++++++-- include/linux/hugetlb.h | 4 +- include/linux/shmem_fs.h | 8 +- include/linux/userfaultfd_k.h | 26 ++++-- include/uapi/linux/userfaultfd.h | 31 ++++++- mm/hugetlb.c | 3 +- mm/internal.h | 13 +++ mm/memory.c | 12 --- mm/shmem.c | 6 +- mm/userfaultfd.c | 103 +++++++++++++++------- tools/testing/selftests/vm/run_vmtests.sh | 16 ++-- tools/testing/selftests/vm/userfaultfd.c | 54 +++++++++++- 12 files changed, 275 insertions(+), 78 deletions(-) -- 2.25.1
