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Date:   Wed, 24 Feb 2021 18:14:15 -0800
From:   Axel Rasmussen <>
To:     Alexander Viro <>,
        Andrea Arcangeli <>,
        Andrew Morton <>,
        Hugh Dickins <>,
        Jerome Glisse <>,
        Joe Perches <>,
        Lokesh Gidra <>,
        Mike Rapoport <>,
        Peter Xu <>, Shaohua Li <>,
        Shuah Khan <>, Wang Qing <>
        Axel Rasmussen <>,
        Cannon Matthews <>,
        "Dr . David Alan Gilbert" <>,
        David Rientjes <>,
        Michel Lespinasse <>,
        Mina Almasry <>,
        Oliver Upton <>
Subject: [PATCH 0/5] userfaultfd: support minor fault handling for shmem


This series is based on top of my series which adds minor fault handling for
hugetlbfs [1]. (And, therefore, it is based on linux-next/akpm and Peter Xu's
series for disabling huge pmd sharing as well.)



See my original series linked above for a detailed overview of minor fault
handling in general. The feature in this series works exactly like the
hugetblfs version (from userspace's perspective).

I'm sending this as a separate series because:

- The original minor fault handling series has been through several rounds of
  review and seems close to being merged, so it seems reasonable to start
  looking at this next step.

- shmem is different enough that this series may require some additional work
  before it's ready, and I don't want to delay the original series
  unnecessarily by bundling them together.

Use Case

In some cases it is useful to have VM memory backed by tmpfs instead of
hugetlbfs. So, this feature will be used to support the same VM live migration
use case described in my original series.

Additionally, Android folks (Lokesh Gidra <>) hope to
optimize the Android JVM garbage collector using this feature (a paper
describing a somewhat similar approach:

Axel Rasmussen (5):
  userfaultfd: support minor fault handling for shmem
  userfaultfd/selftests: use memfd_create for shmem test type
  userfaultfd/selftests: create alias mappings in the shmem test
  userfaultfd/selftests: reinitialize test context in each test
  userfaultfd/selftests: exercise minor fault handling shmem support

 fs/userfaultfd.c                         |   6 +-
 include/linux/shmem_fs.h                 |  26 +-
 include/uapi/linux/userfaultfd.h         |   4 +-
 mm/memory.c                              |   8 +-
 mm/shmem.c                               |  88 +++----
 mm/userfaultfd.c                         |  27 +-
 tools/testing/selftests/vm/userfaultfd.c | 322 +++++++++++++++--------
 7 files changed, 293 insertions(+), 188 deletions(-)


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