Two alternatives for mm async teardown

This RFC series proposes two possible ways for enabling asynchronous mm
teardown.

The first approach, in patch 1, is simply to provide an arch hook in
exit_mm. This has no functional change for archs that don't explicitly
use the hook, and leaves the hard part to arch code (including
accounting, if any).

The second approach, in patches 2 to 4, adds a new syscall to allow an
mm to be asynchronously torn down in the context of another process
(similarly to how process_mrelease works). It also adds an OOM notifier
to prevent the OOM killer from killing processes while the teardown is
in progress.


Claudio Imbrenda (4):
  exit: add arch mmput hook in exit_mm
  kernel/fork.c: implement new process_mmput_async syscall
  mm: wire up the process_mmput_async syscall
  kernel/fork.c: process_mmput_async: stop OOM while freeing memory

 arch/alpha/kernel/syscalls/syscall.tbl      |   2 +
 arch/arm/tools/syscall.tbl                  |   1 +
 arch/arm64/include/asm/unistd.h             |   2 +-
 arch/arm64/include/asm/unistd32.h           |   2 +
 arch/ia64/kernel/syscalls/syscall.tbl       |   2 +
 arch/m68k/kernel/syscalls/syscall.tbl       |   2 +
 arch/microblaze/kernel/syscalls/syscall.tbl |   2 +
 arch/mips/kernel/syscalls/syscall_n32.tbl   |   2 +
 arch/mips/kernel/syscalls/syscall_n64.tbl   |   2 +
 arch/mips/kernel/syscalls/syscall_o32.tbl   |   2 +
 arch/parisc/kernel/syscalls/syscall.tbl     |   2 +
 arch/powerpc/kernel/syscalls/syscall.tbl    |   2 +
 arch/s390/kernel/syscalls/syscall.tbl       |   2 +
 arch/sh/kernel/syscalls/syscall.tbl         |   2 +
 arch/sparc/kernel/syscalls/syscall.tbl      |   2 +
 arch/x86/entry/syscalls/syscall_32.tbl      |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl      |   1 +
 arch/xtensa/kernel/syscalls/syscall.tbl     |   2 +
 include/asm-generic/mmu_context.h           |   4 +
 include/linux/mm_types.h                    |   1 +
 include/linux/syscalls.h                    |   1 +
 include/uapi/asm-generic/unistd.h           |   5 +-
 kernel/exit.c                               |   2 +-
 kernel/fork.c                               | 131 +++++++++++++++++++-
 kernel/sys_ni.c                             |   1 +
 25 files changed, 173 insertions(+), 5 deletions(-)

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2.31.1