Re: [PATCH v1 2/3] mm: process_mrelease: skip LRU movement for exclusive file folios

[Barry Song]

On Fri, Apr 24, 2026 at 3:58 PM David Hildenbrand (Arm)
<david@xxxxxxxxxx> wrote:
>
> On 4/24/26 09:51, Michal Hocko wrote:
> > On Tue 21-04-26 16:02:38, Minchan Kim wrote:
> >> For the process_mrelease reclaim, skip LRU handling for exclusive
> >> file-backed folios since they will be freed soon so pointless
> >> to move around in the LRU.
> >>
> >> This avoids costly LRU movement which accounts for a significant portion
> >> of the time during unmap_page_range.
> >>
> >> -   91.31%     0.00%  mmap_exit_test   [kernel.kallsyms]  [.] exit_mm
> >>      exit_mm
> >>      __mmput
> >>      exit_mmap
> >>      unmap_vmas
> >>    - unmap_page_range
> >>       - 55.75% folio_mark_accessed
> >>          + 48.79% __folio_batch_add_and_move
> >>            4.23% workingset_activation
> >>       + 12.94% folio_remove_rmap_ptes
> >>       + 9.86% page_table_check_clear
> >>       + 3.34% tlb_flush_mmu
> >>         1.06% __page_table_check_pte_clear
> >>
> >> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> >
> > As pointed out in the previous version of the patch. I really dislike
> > this to be mrelease or OOM specific. Behavior. You do not explain why
> > this needs to be this way, except for the performance reasons. My main
> > question is still unanswered (and NAK before this is sorted out). Why
> > this cannot be applied in general for _any_ exiting task. As you argue
> > the memory will just likely go away so why to bother?
>
> I think there was a lengthy discussion involving Johannes from a previous series.
>
> That should be linked here indeed.

For some reason, while looking into Android reclaim performance, I’m
re-reading Minchan’s old series. I guess the lengthy discussion you’re
referring to is the one below:

rfc v1:
https://lore.kernel.org/linux-mm/20250412085852.48524-1-21cnbao@xxxxxxxxx/
rfc v2:
https://lore.kernel.org/all/20250514070820.51793-1-21cnbao@xxxxxxxxx/

In v2, I added a PR_SET_FADE_ON_DEATH option so that Android can
enable it while other users can leave it disabled.

Maybe there’s a chance to wake it up again?

> Cheers,
>
> David
>

Best Regards
Barry