linux-kernel - Re: [PATCH v8 3/3] mm/vmscan: avoid split lazyfree THP during shrink_folio

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Date: Sat, 22 Jun 2024 18:00:57 +0800
From: Lance Yang <ioworker0@...il.com>
To: david@...hat.com,
	akpm@...ux-foundation.org
Cc: 21cnbao@...il.com,
	baolin.wang@...ux.alibaba.com,
	fengwei.yin@...el.com,
	ioworker0@...il.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,
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	songmuchun@...edance.com,
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	xiehuan09@...il.com,
	ziy@...dia.com,
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Subject: Re: [PATCH v8 3/3] mm/vmscan: avoid split lazyfree THP during shrink_folio_list()

Hi Andrew,

I made some minor changes suggested by David[1]. Could you please fold the
following changes into this patch?

[1] https://lore.kernel.org/linux-mm/e7c0aff1-b690-4926-9a34-4e32c9f3faaa@redhat.com/

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4b2817bb2c7d..0cb52ae29259 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2693,21 +2693,11 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma,
 					    unsigned long addr, pmd_t *pmdp,
 					    struct folio *folio)
 {
-	VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio);
-	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
-
 	struct mm_struct *mm = vma->vm_mm;
 	int ref_count, map_count;
 	pmd_t orig_pmd = *pmdp;
 	struct page *page;
 
-	if (unlikely(!pmd_present(orig_pmd) || !pmd_trans_huge(orig_pmd)))
-		return false;
-
-	page = pmd_page(orig_pmd);
-	if (unlikely(page_folio(page) != folio))
-		return false;
-
 	if (folio_test_dirty(folio) || pmd_dirty(orig_pmd))
 		return false;
 
diff --git a/mm/rmap.c b/mm/rmap.c
index df1a43295c85..b358501fb7e8 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1678,9 +1678,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 
 			if (flags & TTU_SPLIT_HUGE_PMD) {
 				/*
-				 * We temporarily have to drop the PTL and start
-				 * once again from that now-PTE-mapped page
-				 * table.
+				 * We temporarily have to drop the PTL and
+				 * restart so we can process the PTE-mapped THP.
 				 */
 				split_huge_pmd_locked(vma, pvmw.address,
 						      pvmw.pmd, false, folio);
-- 

Thanks,
Lance