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

[Minchan Kim <minchan@kernel.org>]

On Wed, Apr 22, 2026 at 03:22:46PM +0800, Baolin Wang wrote:
> 
> 
> On 4/22/26 7:02 AM, 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@kernel.org>
> > ---
> >   mm/memory.c | 13 ++++++++++++-
> >   1 file changed, 12 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 2f815a34d924..fcb57630bb8d 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -1640,6 +1640,8 @@ static __always_inline void zap_present_folio_ptes(struct mmu_gather *tlb,
> >   	bool delay_rmap = false;
> >   	if (!folio_test_anon(folio)) {
> > +		bool skip_mark_accessed;
> > +
> >   		ptent = get_and_clear_full_ptes(mm, addr, pte, nr, tlb->fullmm);
> >   		if (pte_dirty(ptent)) {
> >   			folio_mark_dirty(folio);
> > @@ -1648,7 +1650,16 @@ static __always_inline void zap_present_folio_ptes(struct mmu_gather *tlb,
> >   				*force_flush = true;
> >   			}
> >   		}
> > -		if (pte_young(ptent) && likely(vma_has_recency(vma)))
> > +
> > +		/*
> > +		 * 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.
> > +		 */
> > +		skip_mark_accessed = mm_flags_test(MMF_UNSTABLE, mm) &&
> > +				     !folio_maybe_mapped_shared(folio);
> > +		if (likely(!skip_mark_accessed) && pte_young(ptent) &&
> > +		    likely(vma_has_recency(vma)))
> >   			folio_mark_accessed(folio);
> >   		rss[mm_counter(folio)] -= nr;
> >   	} else {
> 
> Seems we should also skip marking exclusive pmd-sized folios as accessed in
> zap_huge_pmd_folio().

Good catch.

Will update in next revision.

Thank you.