Re: [PATCH v7 4/4] mm/vmscan: avoid split lazyfree THP during shrink_folio_list()

[Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>]

On 2024/6/13 15:28, Lance Yang wrote:
> Hi Andrew,
>
> I'd like to fix the bug[1] I mentioned previously. Could you please fold the
> following changes into this patch?
>
> [1] https://lore.kernel.org/linux-mm/20240613065521.15960-1-ioworker0@xxxxxxxxx/
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index f409ea9fcc18..425374ae06ed 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2707,10 +2707,8 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma,
>   	if (unlikely(page_folio(page) != folio))
>   		return false;
>   
> -	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) {
> -		folio_set_swapbacked(folio);
> +	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd))
>   		return false;
> -	}
>   
>   	orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp);
>   
> @@ -2737,10 +2735,8 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma,
>   	 *
>   	 * The only folio refs must be one from isolation plus the rmap(s).
>   	 */
> -	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd))
> -		folio_set_swapbacked(folio);
> -
> -	if (folio_test_swapbacked(folio) || ref_count != map_count + 1) {
> +	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) ||
> +	    ref_count != map_count + 1) {
>   		set_pmd_at(mm, addr, pmdp, orig_pmd);
>   		return false;
>   	}
> diff --git a/mm/rmap.c b/mm/rmap.c
> index b9e5943c8349..393e2c11c44c 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1824,12 +1824,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>   			 */
>   			if (unlikely(folio_test_swapbacked(folio) !=
>   					folio_test_swapcache(folio))) {
> -				/*
> -				 * unmap_huge_pmd_locked() will unmark a
> -				 * PMD-mapped folio as lazyfree if the folio or
> -				 * its PMD was redirtied.
> -				 */
> -				WARN_ON_ONCE(!pmd_mapped);
> +				WARN_ON_ONCE(1);
>   				goto walk_done_err;
>   			}
>   

You can also drop the unused 'pmd_mapped' variable now.