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

[David Hildenbrand (Arm)]

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