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

[Baolin Wang <baolin.wang@linux.alibaba.com>]

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().