Re: [RFC PATCH 0/7] mm: defer address-space teardown of large exiting processes to a kthread

On 7/19/26 19:54, Aditya Sharma wrote:

Address-space teardown on process exit runs synchronously in the dying
task's context: exit_mm() -> mmput() -> __mmput() -> exit_mmap() walks
page tables, updates rmap, frees the RSS and drops file references, all
on the exiting CPU. For a multi-GB process that is hundreds of
milliseconds of exit-path latency, paid by whoever is waiting on the
death: a supervisor's kill-and-respawn cycle, a shell's waitpid(), an
orchestrator reaping a fleet of workers. On the test box below, killing
a 16GB process costs ~280ms before the parent's waitpid() returns.

This series adds CONFIG_ASYNC_MM_TEARDOWN: an opt-in, default-off path
that defers __mmput() of large exiting processes to a dedicated kernel
thread (mm_reaper), so the exiting CPU is released as soon as the task
is reaped and the teardown runs off to the side.

QEMU has an rather short implementation for async teardown using
clone(CLONE_VM), which is IIRC essentially the result of Claudios previous
kernel work you note below.

So nothing got merged because the problem was solvable in userspace.

Without something like CONFIG_ASYNC_MM_TEARDOWN in the kernel.

[1] https://github.com/qemu/qemu/blob/master/system/async-teardown.c

-- 
Cheers,

David