Re: [PATCH 1/1] mm/vmscan: prevent MGLRU reclaim from pinning address space

[Lorenzo Stoakes (Oracle)]

On Sun, Mar 22, 2026 at 12:08:43AM -0700, Suren Baghdasaryan wrote:
> When shrinking lruvec, MGLRU pins address space before walking it.
> This is excessive since all it needs for walking the page range is
> a stable mm_struct to be able to take and release mmap_read_lock and
> a stable mm->mm_mt tree to walk. This address space pinning results
> in delays when releasing the memory of a dying process. This also
> prevents mm reapers (both in-kernel oom-reaper and userspace
> process_mrelease()) from doing their job during MGLRU scan because
> they check task_will_free_mem() which will yield negative result due
> to the elevated mm->mm_users.
>
> Replace unnecessary address space pinning with mm_struct pinning by
> replacing mmget/mmput with mmgrab/mmdrop calls. mm_mt is contained
> within mm_struct itself, therefore it won't be freed as long as
> mm_struct is stable and it won't change during the walk because
> mmap_read_lock is being held.
>
> Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks")
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>

Oh and sorry, missed this - do we need a 'Fixed' for something that's just a
perf improvement?

This doesn't seem buggy?

Thanks, Lorenzo