linux-kernel - Re: [PATCH v7 4/4] mm/vmscan: avoid split lazyfree THP during shrink_folio

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Date: Thu, 13 Jun 2024 16:20:36 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Lance Yang <ioworker0@...il.com>, akpm@...ux-foundation.org
Cc: 21cnbao@...il.com, david@...hat.com, fengwei.yin@...el.com,
 libang.li@...group.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 maskray@...gle.com, mhocko@...e.com, minchan@...nel.org, peterx@...hat.com,
 ryan.roberts@....com, shy828301@...il.com, sj@...nel.org,
 songmuchun@...edance.com, wangkefeng.wang@...wei.com, willy@...radead.org,
 xiehuan09@...il.com, ziy@...dia.com, zokeefe@...gle.com
Subject: Re: [PATCH v7 4/4] mm/vmscan: avoid split lazyfree THP during
 shrink_folio_list()



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@gmail.com/
> 
> 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.