[PATCH 0/2] userspace memory reaping using process_madvise

[Suren Baghdasaryan]

When a process is being killed it might be in an uninterruptible sleep
which leads to an unpredictable delay in its memory reclaim. In low memory
situations, when it's important to free up memory quickly, such delay is
problematic. Kernel solves this problem with oom-reaper thread which
performs memory reclaim even when the victim process is not runnable.
Userspace currently lacks such mechanisms and the need and potential
solutions were discussed before (see links below).
This patchset provides a mechanism to perform memory reclaim of an
external process using process_madvise(MADV_DONTNEED). The chosen
mechanism is the result of the latest discussion at [4].
The first patch adds PMADV_FLAG_RANGE flag for process_madvise to operate
on large address ranges spanning multiple VMAs. Currently it supports only
the entire memory of a process. This is done to keep things simple and
since it's the only real usecase we currently know of. In the future this
can be developed further to support other large ranges. One way to do that
is suggested in [5].
The second patch enables MADV_DONTNEED behavior for process_madvise to
perform memory reclaim of an external process.

1. https://patchwork.kernel.org/cover/10894999
2. https://lwn.net/Articles/787217
3. https://lore.kernel.org/linux-api/CAJuCfpGz1kPM3G1gZH+09Z7aoWKg05QSAMMisJ7H5MdmRrRhNQ@xxxxxxxxxxxxxx
4. https://lkml.org/lkml/2020/11/13/849
5. https://lkml.org/lkml/2020/11/18/1076

Suren Baghdasaryan (2):
  mm/madvise: allow process_madvise operations on entire memory range
  mm/madvise: add process_madvise MADV_DONTNEER support

 arch/alpha/include/uapi/asm/mman.h           |  4 +
 arch/mips/include/uapi/asm/mman.h            |  4 +
 arch/parisc/include/uapi/asm/mman.h          |  4 +
 arch/xtensa/include/uapi/asm/mman.h          |  4 +
 fs/io_uring.c                                |  2 +-
 include/linux/mm.h                           |  3 +-
 include/uapi/asm-generic/mman-common.h       |  4 +
 mm/madvise.c                                 | 81 ++++++++++++++++++--
 tools/include/uapi/asm-generic/mman-common.h |  4 +
 9 files changed, 101 insertions(+), 9 deletions(-)

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2.29.2.454.gaff20da3a2-goog