[RFC PATCH v2 0/5] userfaultfd: support access/write hints

From: Nadav Amit <nadav.amit@gmail.com>
To: linux-mm@kvack.org
Cc: Nadav Amit <namit@vmware.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Hugh Dickins <hughd@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Axel Rasmussen <axelrasmussen@google.com>,
	Peter Xu <peterx@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Mike Rapoport <rppt@linux.ibm.com>
Subject: [RFC PATCH v2 0/5] userfaultfd: support access/write hints
Date: Sun, 19 Jun 2022 16:34:44 -0700	[thread overview]
Message-ID: <20220619233449.181323-1-namit@vmware.com> (raw)

From: Nadav Amit <namit@vmware.com>

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.

Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>

Nadav Amit (5):
  userfaultfd: introduce uffd_flags
  userfaultfd: introduce access-likely mode for copy/wp operations
  userfaultfd: introduce write-likely mode for copy/wp operations
  userfaultfd: zero access/write hints
  selftest/userfaultfd: test read/write hints

 fs/userfaultfd.c                         |  57 ++++++++---
 include/linux/hugetlb.h                  |   4 +-
 include/linux/shmem_fs.h                 |   8 +-
 include/linux/userfaultfd_k.h            |  25 +++--
 include/uapi/linux/userfaultfd.h         |  33 ++++++-
 mm/hugetlb.c                             |   6 +-
 mm/shmem.c                               |   9 +-
 mm/userfaultfd.c                         | 118 +++++++++++++++++------
 tools/testing/selftests/vm/userfaultfd.c |  26 +++++
 9 files changed, 226 insertions(+), 60 deletions(-)

-- 
2.25.1