Skip to contentSkip to conversation

mm/rmap: Refactor try_to_unmap_one

PATCH Applied Dev Jain 3 participants 8 messages Jul 30 – Jul 31

Subsystems (3)
Memory management HugeTLB MM rmap
lore
Share & tools
lore

Dev Jain

author
#0 lore raw

v4 cover mm/rmap: Refactor try_to_unmap_one

In preparation for batching anonymous large folio unmapping to optimize it, refactor try_to_unmap_one. This series refactors hugetlb, anon-lazyfree and anon-swapbacked logic into their own functions, significantly reducing the length of the huge try_to_unmap_one.

---
Based on mm-unstable (d8c677ce1220b0db119ada6c6f9762c07c4d8aca).

Split out from
https://lore.kernel.org/all/[email protected]/

mm-selftests pass on arm64, built on arm64 and x86.

v3->v4:
- Tighten comment around TTU_HWPOISON
- try_to_unmap_hugetlb_one -> try_to_unmap_poisoned_hugetlb_one
- VM_WARN_ON -> VM_WARN_ON_ONCE

v2->v3:
- Patch 2: fix comment to say that TTU_HWPOISON can be true for small folios only in try_to_unmap_one, since hugetlb bits are now refactored away
- Patch 5: Directly do if (WARN_ON_ONCE())
- Rebase on latest mm-unstable to resolve conflicts with 30c83145c5b3 ("mm: rename uffd-wp PTE accessors to uffd")

v1->v2:
- constify ttu flags in try_to_unmap_hugetlb_one, move const variables up
- Assert address passed to try_to_unmap_hugetlb_one equals pvmw.address
- Patch 3: code and comment polishing, do the stat update in the function
- Remove unnecessary inline hints, remove set_swp_pte_at, instead have swp_pte_prepare + set_ptes. Rename subpage -> page. constify anon_exclusive.
- Do pte restoration in caller

Dev Jain (5):
mm/rmap: convert page -> folio for hwpoison checks mm/rmap: Add try_to_unmap_poisoned_hugetlb_one mm/rmap: refactor some code around lazyfree folio unmapping mm/rmap: refactor anon folio unmap in try_to_unmap_one mm/rmap: add anon folio unmap dispatcher

 include/linux/hugetlb.h |   1 +
 mm/rmap.c               | 415 ++++++++++++++++++++++------------------
 2 files changed, 232 insertions(+), 184 deletions(-)
Signature · 1 line
2.43.0
author
#1 lore raw

PATCH v4 1/5 mm/rmap: convert page -> folio for hwpoison checks

try_to_unmap() receives hugetlb folios only from the hwpoison path. hugetlb_update_hwpoison() sets the hugetlb folio's head-page hwpoison bit, and page_vma_mapped_walk() reports the hugetlb mapping at the head PFN, so the previous PageHWPoison(subpage) check happened to work for hugetlb.

For non-hugetlb folios, unmap_poisoned_folio() currently rejects large folios before calling try_to_unmap(). Hence it is always the case that if try_to_unmap_one() handles an hwpoisoned folio, then the head page is marked with the poison bit.

Therefore, convert the poisoned subpage checks to folio_test_hwpoison().

No functional change intended, except that, while at it, convert VM_BUG_* to VM_WARN_*.

Reviewed-by Lorenzo Stoakes (ARM) <[email protected]>
Acked-by David Hildenbrand (Arm) <[email protected]>
Signed-off-by Dev Jain <[email protected]>
---
 mm/rmap.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)
mm/rmap.c +6 -4
index e854679553b9..77be9fcffa99 100644
@@ -2122,10 +2122,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			bool anon = folio_test_anon(folio);
 
 			/*
-			 * The try_to_unmap() is only passed a hugetlb page
-			 * in the case where the hugetlb page is poisoned.
+			 * The try_to_unmap() is only passed a hugetlb folio
+			 * in the case where the hugetlb folio contains a
+			 * poisoned page.
 			 */
-			VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage);
+			VM_WARN_ON_FOLIO(!folio_test_hwpoison(folio), folio);
 			/*
 			 * huge_pmd_unshare may unmap an entire PMD page.
 			 * There is no way of knowing exactly which PMDs may

@@ -2204,7 +2205,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		/* Update high watermark before we lower rss */
 		update_hiwater_rss(mm);
 
-		if (PageHWPoison(subpage) && (flags & TTU_HWPOISON)) {
+		/* unmap_poisoned_folio() only refs order-0 or hugetlb folios */
+		if (folio_test_hwpoison(folio) && (flags & TTU_HWPOISON)) {
 			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
 			if (folio_test_hugetlb(folio)) {
 				hugetlb_count_sub(folio_nr_pages(folio), mm);
Signature · 1 line
2.43.0
Reviewed-by on v4 1/5
#2 lore raw

Re: [PATCH v4 1/5] mm/rmap: convert page -> folio for hwpoison checks

Quoted 11 lines · Dev Jain

try_to_unmap() receives hugetlb folios only from the hwpoison path. hugetlb_update_hwpoison() sets the hugetlb folio's head-page hwpoison bit, and page_vma_mapped_walk() reports the hugetlb mapping at the head PFN, so the previous PageHWPoison(subpage) check happened to work for hugetlb.

For non-hugetlb folios, unmap_poisoned_folio() currently rejects large folios before calling try_to_unmap(). Hence it is always the case that if try_to_unmap_one() handles an hwpoisoned folio, then the head page is marked with the poison bit.

Quoted 8 lines

Therefore, convert the poisoned subpage checks to folio_test_hwpoison().

No functional change intended, except that, while at it, convert VM_BUG_* to VM_WARN_*.

Reviewed-by Lorenzo Stoakes (ARM) <[email protected]>
Acked-by David Hildenbrand (Arm) <[email protected]>
Signed-off-by Dev Jain <[email protected]>
Reviewed-by Anshuman Khandual <[email protected]>
Quoted 36 lines
---
 mm/rmap.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)
mm/rmap.c +6 -4
index e854679553b9..77be9fcffa99 100644
@@ -2122,10 +2122,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			bool anon = folio_test_anon(folio);
 
 			/*
-			 * The try_to_unmap() is only passed a hugetlb page
-			 * in the case where the hugetlb page is poisoned.
+			 * The try_to_unmap() is only passed a hugetlb folio
+			 * in the case where the hugetlb folio contains a
+			 * poisoned page.
 			 */
-			VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage);
+			VM_WARN_ON_FOLIO(!folio_test_hwpoison(folio), folio);
 			/*
 			 * huge_pmd_unshare may unmap an entire PMD page.
 			 * There is no way of knowing exactly which PMDs may

@@ -2204,7 +2205,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		/* Update high watermark before we lower rss */
 		update_hiwater_rss(mm);
 
-		if (PageHWPoison(subpage) && (flags & TTU_HWPOISON)) {
+		/* unmap_poisoned_folio() only refs order-0 or hugetlb folios */
+		if (folio_test_hwpoison(folio) && (flags & TTU_HWPOISON)) {
 			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
 			if (folio_test_hugetlb(folio)) {
 				hugetlb_count_sub(folio_nr_pages(folio), mm);
Signature · 1 line
2.43.0
author
#3 lore raw

PATCH v4 2/5 mm/rmap: Add try_to_unmap_poisoned_hugetlb_one

In reply to Dev Jain

Simplify try_to_unmap_one() by separating the hugetlb parts into try_to_unmap_poisoned_hugetlb_one().

To understand the correctness of the refactoring, the following points are noted:

1. try_to_unmap() is called for hugetlb folios only when they are hwpoisoned.

2. A hugetlb VMA cannot be mlocked.

3. page_vma_mapped_walk() returns at most one hugetlb mapping in a VMA, and that mapping points at the head PFN.

4. We won't ever process a softleaf entry that encodes a hugetlb folio; hugetlb folios are never swapped out, migration entries will be skipped (PVMW_MIGRATION not passed), and device-exclusive does not work for hugetlb.

5. The hwpoison entry is constructed from the poisoned folio, just as in the pre-refactor code. Any previous uffd-wp state is deliberately not preserved for the hwpoison entry.

6. TTU_HWPOISON is always present; for it to not be present, either the folio has to be in swapcache, or mapping_can_writeback() is true (see unmap_poisoned_folio), none of which is true for hugetlb folios.

7. Hugetlb uses separate counters from normal rss counters, therefore update_highwater_rss() need not be called.

While at it:

- Change VM_BUG_* to VM_WARN_*.

- Do not declare variables which are only used once.

- Constify some variables.

- Add some more VM_WARN_* to assert some invariants.

Except the above 4 points, no functional change intended.

Reviewed-by Lorenzo Stoakes (ARM) <[email protected]>
Suggested-by David Hildenbrand (Arm) <[email protected]>
Acked-by David Hildenbrand (Arm) <[email protected]>
Signed-off-by Dev Jain <[email protected]>
---
 include/linux/hugetlb.h |   1 +
 mm/rmap.c               | 180 ++++++++++++++++++++++------------------
 2 files changed, 98 insertions(+), 83 deletions(-)
include/linux/hugetlb.h +1 -0
index 6ca232a61643..16c4c4caa126 100644
@@ -1270,6 +1270,7 @@ static inline void hugetlb_count_sub(long l, struct mm_struct *mm)
 }
 
 pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
+unsigned long huge_pte_dirty(pte_t pte);
 
 static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
 					  unsigned long addr, pte_t *ptep)
mm/rmap.c +97 -83

236 lines not on this page · raw message

Signature · 1 line
2.43.0
author
#4 lore raw

PATCH v4 3/5 mm/rmap: refactor some code around lazyfree folio unmapping

In reply to Dev Jain

For lazyfree folio unmapping, after clearing the ptes we must abort the operation if the folio got dirtied or it has unexpected references.

Refactor this logic into a function which will return whether we need to abort or not.

If we abort, we restore the ptes and bail out of try_to_unmap_one. Otherwise adjust the rss stats of the mm and jump to a label.

Also rename that label from "discard" to "finish_unmap"; the former is appropriate in the lazyfree context, but the code following the label is executed for other successful unmap code paths too, so 'discard' does not sound correct for them.

No functional change intended.

Acked-by David Hildenbrand (Arm) <[email protected]>
Signed-off-by Dev Jain <[email protected]>
---
 mm/rmap.c | 87 ++++++++++++++++++++++++++++++-------------------------
 1 file changed, 48 insertions(+), 39 deletions(-)
mm/rmap.c +48 -39
index 9cb496d7b375..dd1309d72e37 100644
@@ -2068,6 +2068,50 @@ static bool try_to_unmap_poisoned_hugetlb_one(struct folio *folio,
 	return ret;
 }
 
+static bool ttu_anon_lazyfree_folio(struct vm_area_struct *vma,
+		struct folio *folio, unsigned long nr_pages)
+{
+	int ref_count, map_count;
+
+	/*
+	 * Synchronize with gup_pte_range():
+	 * - clear PTE; barrier; read refcount
+	 * - inc refcount; barrier; read PTE
+	 */
+	smp_mb();
+
+	ref_count = folio_ref_count(folio);
+	map_count = folio_mapcount(folio);
+
+	/*
+	 * Order reads for page refcount and dirty flag
+	 * (see comments in __remove_mapping()).
+	 */
+	smp_rmb();
+
+	if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) {
+		/*
+		 * redirtied either using the page table or a previously
+		 * obtained GUP reference.
+		 */
+		folio_set_swapbacked(folio);
+		return false;
+	}
+
+	/*
+	 * Additional references could be due to GUP or speculative lookups.
+	 * GUP users must mark the folio dirty if there was a modification.
+	 * This folio cannot be reclaimed right now either way, so act just
+	 * like nothing happened. We'll come back here later and detect if the
+	 * folio was dirtied when the additional reference is gone.
+	 */
+	if (ref_count != 1 + map_count)
+		return false;
+
+	add_mm_counter(vma->vm_mm, MM_ANONPAGES, -nr_pages);
+	return true;
+}
+
 /*
  * @arg: enum ttu_flags will be passed to this argument
  */

@@ -2261,47 +2305,12 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 
 			/* MADV_FREE page check */
 			if (!folio_test_swapbacked(folio)) {
-				int ref_count, map_count;
-
-				/*
-				 * Synchronize with gup_pte_range():
-				 * - clear PTE; barrier; read refcount
-				 * - inc refcount; barrier; read PTE
-				 */
-				smp_mb();
-
-				ref_count = folio_ref_count(folio);
-				map_count = folio_mapcount(folio);
-
-				/*
-				 * Order reads for page refcount and dirty flag
-				 * (see comments in __remove_mapping()).
-				 */
-				smp_rmb();
-
-				if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) {
-					/*
-					 * redirtied either using the page table or a previously
-					 * obtained GUP reference.
-					 */
-					set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
-					folio_set_swapbacked(folio);
-					goto walk_abort;
-				} else if (ref_count != 1 + map_count) {
-					/*
-					 * Additional reference. Could be a GUP reference or any
-					 * speculative reference. GUP users must mark the folio
-					 * dirty if there was a modification. This folio cannot be
-					 * reclaimed right now either way, so act just like nothing
-					 * happened.
-					 * We'll come back here later and detect if the folio was
-					 * dirtied when the additional reference is gone.
-					 */
+				if (!ttu_anon_lazyfree_folio(vma, folio,
+							     nr_pages)) {
 					set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
 					goto walk_abort;
 				}
-				add_mm_counter(mm, MM_ANONPAGES, -nr_pages);
-				goto discard;
+				goto finish_unmap;
 			}
 
 			if (folio_dup_swap(folio, subpage) < 0) {

@@ -2359,7 +2368,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			 */
 			add_mm_counter(mm, mm_counter_file(folio), -nr_pages);
 		}
-discard:
+finish_unmap:
 		folio_remove_rmap_ptes(folio, subpage, nr_pages, vma);
 		if (vma->vm_flags & VM_LOCKED)
 			mlock_drain_local();
Signature · 1 line
2.43.0
author
#5 lore raw

PATCH v4 4/5 mm/rmap: refactor anon folio unmap in try_to_unmap_one

In reply to Dev Jain

Refactor anonymous swapbacked folio unmap to ttu_anon_swapbacked_folio(). While at it, rename the remaining subpage variables to page; folios have pages, not subpages.

No functional change intended.

Acked-by David Hildenbrand (Arm) <[email protected]>
Signed-off-by Dev Jain <[email protected]>
---
 mm/rmap.c | 115 ++++++++++++++++++++++++++++++++----------------------
 1 file changed, 68 insertions(+), 47 deletions(-)
mm/rmap.c +68 -47
index dd1309d72e37..15efde4d1fc9 100644
@@ -2112,6 +2112,66 @@ static bool ttu_anon_lazyfree_folio(struct vm_area_struct *vma,
 	return true;
 }
 
+static pte_t swp_pte_prepare(swp_entry_t entry, pte_t old_pte,
+		bool anon_exclusive)
+{
+	pte_t swp_pte = swp_entry_to_pte(entry);
+
+	if (anon_exclusive)
+		swp_pte = pte_swp_mkexclusive(swp_pte);
+
+	if (likely(pte_present(old_pte))) {
+		if (pte_soft_dirty(old_pte))
+			swp_pte = pte_swp_mksoft_dirty(swp_pte);
+		if (pte_uffd(old_pte))
+			swp_pte = pte_swp_mkuffd(swp_pte);
+	} else {
+		/* Device-exclusive entry */
+		if (pte_swp_soft_dirty(old_pte))
+			swp_pte = pte_swp_mksoft_dirty(swp_pte);
+		if (pte_swp_uffd(old_pte))
+			swp_pte = pte_swp_mkuffd(swp_pte);
+	}
+
+	return swp_pte;
+}
+
+static bool ttu_anon_swapbacked_folio(struct vm_area_struct *vma,
+		struct folio *folio, struct page *page, unsigned long address,
+		pte_t *ptep, pte_t pteval)
+{
+	const bool anon_exclusive = folio_test_anon(folio) &&
+				    PageAnonExclusive(page);
+	swp_entry_t entry = page_swap_entry(page);
+	struct mm_struct *mm = vma->vm_mm;
+
+	if (folio_dup_swap(folio, page) < 0)
+		return false;
+
+	/*
+	 * arch_unmap_one() is expected to be a NOP on
+	 * architectures where we could have PFN swap PTEs,
+	 * so we'll not check/care.
+	 */
+	if (arch_unmap_one(mm, vma, address, pteval) < 0) {
+		folio_put_swap(folio, page);
+		return false;
+	}
+
+	/* See folio_try_share_anon_rmap(): clear PTE first. */
+	if (anon_exclusive && folio_try_share_anon_rmap_pte(folio, page)) {
+		folio_put_swap(folio, page);
+		return false;
+	}
+
+	mm_prepare_for_swap_entries(mm);
+	dec_mm_counter(mm, MM_ANONPAGES);
+	inc_mm_counter(mm, MM_SWAPENTS);
+	set_pte_at(mm, address, ptep,
+		   swp_pte_prepare(entry, pteval, anon_exclusive));
+	return true;
+}
+
 /*
  * @arg: enum ttu_flags will be passed to this argument
  */

@@ -2120,9 +2180,9 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 {
 	struct mm_struct *mm = vma->vm_mm;
 	DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
-	bool anon_exclusive, ret = true;
+	bool ret = true;
 	pte_t pteval;
-	struct page *subpage;
+	struct page *page;
 	struct mmu_notifier_range range;
 	enum ttu_flags flags = (enum ttu_flags)(long)arg;
 	unsigned long nr_pages = 1, end_addr;

@@ -2233,9 +2293,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			pfn = softleaf_to_pfn(entry);
 		}
 
-		subpage = folio_page(folio, pfn - folio_pfn(folio));
-		anon_exclusive = folio_test_anon(folio) &&
-				 PageAnonExclusive(subpage);
+		page = folio_page(folio, pfn - folio_pfn(folio));
 
 		if (likely(pte_present(pteval))) {
 			nr_pages = folio_unmap_pte_batch(folio, &pvmw, flags, pteval);

@@ -2274,7 +2332,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 
 		/* unmap_poisoned_folio() only refs order-0 folios */
 		if (folio_test_hwpoison(folio) && (flags & TTU_HWPOISON)) {
-			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
+			pteval = swp_entry_to_pte(make_hwpoison_entry(page));
 			dec_mm_counter(mm, mm_counter(folio));
 			set_pte_at(mm, address, pvmw.pte, pteval);
 		} else if (likely(pte_present(pteval)) && pte_unused(pteval) &&

@@ -2291,8 +2349,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			 */
 			dec_mm_counter(mm, mm_counter(folio));
 		} else if (folio_test_anon(folio)) {
-			swp_entry_t entry = page_swap_entry(subpage);
-			pte_t swp_pte;
 			/*
 			 * Store the swap location in the pte.
 			 * See handle_pte_fault() ...

@@ -2313,47 +2369,12 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 				goto finish_unmap;
 			}
 
-			if (folio_dup_swap(folio, subpage) < 0) {
-				set_pte_at(mm, address, pvmw.pte, pteval);
-				goto walk_abort;
-			}
-
-			/*
-			 * arch_unmap_one() is expected to be a NOP on
-			 * architectures where we could have PFN swap PTEs,
-			 * so we'll not check/care.
-			 */
-			if (arch_unmap_one(mm, vma, address, pteval) < 0) {
-				folio_put_swap(folio, subpage);
-				set_pte_at(mm, address, pvmw.pte, pteval);
-				goto walk_abort;
-			}
-
-			/* See folio_try_share_anon_rmap(): clear PTE first. */
-			if (anon_exclusive &&
-			    folio_try_share_anon_rmap_pte(folio, subpage)) {
-				folio_put_swap(folio, subpage);
+			if (!ttu_anon_swapbacked_folio(vma, folio, page, address,
+						pvmw.pte, pteval)) {
 				set_pte_at(mm, address, pvmw.pte, pteval);
 				goto walk_abort;
 			}
-			mm_prepare_for_swap_entries(mm);
-			dec_mm_counter(mm, MM_ANONPAGES);
-			inc_mm_counter(mm, MM_SWAPENTS);
-			swp_pte = swp_entry_to_pte(entry);
-			if (anon_exclusive)
-				swp_pte = pte_swp_mkexclusive(swp_pte);
-			if (likely(pte_present(pteval))) {
-				if (pte_soft_dirty(pteval))
-					swp_pte = pte_swp_mksoft_dirty(swp_pte);
-				if (pte_uffd(pteval))
-					swp_pte = pte_swp_mkuffd(swp_pte);
-			} else {
-				if (pte_swp_soft_dirty(pteval))
-					swp_pte = pte_swp_mksoft_dirty(swp_pte);
-				if (pte_swp_uffd(pteval))
-					swp_pte = pte_swp_mkuffd(swp_pte);
-			}
-			set_pte_at(mm, address, pvmw.pte, swp_pte);
+			goto finish_unmap;
 		} else {
 			/*
 			 * This is a locked file-backed folio,

@@ -2369,7 +2390,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			add_mm_counter(mm, mm_counter_file(folio), -nr_pages);
 		}
 finish_unmap:
-		folio_remove_rmap_ptes(folio, subpage, nr_pages, vma);
+		folio_remove_rmap_ptes(folio, page, nr_pages, vma);
 		if (vma->vm_flags & VM_LOCKED)
 			mlock_drain_local();
 		folio_put_refs(folio, nr_pages);
Signature · 1 line
2.43.0
author
#6 lore raw

PATCH v4 5/5 mm/rmap: add anon folio unmap dispatcher

In reply to Dev Jain

Add ttu_anon_folio() as the common entry point for anonymous folio unmapping. It dispatches to the lazyfree or swapbacked helper as appropriate.

Keep restoration of cleared PTEs in the caller, where the PTEs were removed.

No functional change intended.

Acked-by David Hildenbrand (Arm) <[email protected]>
Signed-off-by Dev Jain <[email protected]>
---
 mm/rmap.c | 45 +++++++++++++++++++++++----------------------
 1 file changed, 23 insertions(+), 22 deletions(-)
mm/rmap.c +23 -22
index 15efde4d1fc9..867db2b61573 100644
@@ -2172,6 +2172,26 @@ static bool ttu_anon_swapbacked_folio(struct vm_area_struct *vma,
 	return true;
 }
 
+static bool ttu_anon_folio(struct vm_area_struct *vma, struct folio *folio,
+		struct page *page, unsigned long address, pte_t *ptep,
+		pte_t pteval, unsigned long nr_pages)
+{
+	/*
+	 * Store the swap location in the pte.
+	 * See handle_pte_fault() ...
+	 */
+	if (WARN_ON_ONCE(folio_test_swapbacked(folio) !=
+			 folio_test_swapcache(folio)))
+		return false;
+
+	if (!folio_test_swapbacked(folio))
+		return ttu_anon_lazyfree_folio(vma, folio, nr_pages);
+
+	/* nr_pages > 1 not supported yet */
+	return ttu_anon_swapbacked_folio(vma, folio, page, address, ptep,
+					 pteval);
+}
+
 /*
  * @arg: enum ttu_flags will be passed to this argument
  */

@@ -2349,31 +2369,12 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			 */
 			dec_mm_counter(mm, mm_counter(folio));
 		} else if (folio_test_anon(folio)) {
-			/*
-			 * Store the swap location in the pte.
-			 * See handle_pte_fault() ...
-			 */
-			if (unlikely(folio_test_swapbacked(folio) !=
-					folio_test_swapcache(folio))) {
-				WARN_ON_ONCE(1);
+			if (!ttu_anon_folio(vma, folio, page, address,
+					    pvmw.pte, pteval, nr_pages)) {
+				set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
 				goto walk_abort;
 			}
 
-			/* MADV_FREE page check */
-			if (!folio_test_swapbacked(folio)) {
-				if (!ttu_anon_lazyfree_folio(vma, folio,
-							     nr_pages)) {
-					set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
-					goto walk_abort;
-				}
-				goto finish_unmap;
-			}
-
-			if (!ttu_anon_swapbacked_folio(vma, folio, page, address,
-						pvmw.pte, pteval)) {
-				set_pte_at(mm, address, pvmw.pte, pteval);
-				goto walk_abort;
-			}
 			goto finish_unmap;
 		} else {
 			/*
Signature · 1 line
2.43.0
maintainer
#7 lore raw
In reply to Dev Jain
Quoted 5 lines · On Thu, 30 Jul 2026 09:45:51 +0000 Dev Jain <[email protected]> wrote:

In preparation for batching anonymous large folio unmapping to optimize it, refactor try_to_unmap_one. This series refactors hugetlb, anon-lazyfree and anon-swapbacked logic into their own functions, significantly reducing the length of the huge try_to_unmap_one.

Thanks, updated.

Quoted 5 lines

v3->v4:
- Tighten comment around TTU_HWPOISON
- try_to_unmap_hugetlb_one -> try_to_unmap_poisoned_hugetlb_one
- VM_WARN_ON -> VM_WARN_ON_ONCE

Here's how v4 altered mm.git:

 mm/rmap.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
mm/rmap.c renamed from mm/rmap.c~b +5 -5
@@ -1978,7 +1978,7 @@ static inline unsigned int folio_unmap_p
 				     FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY);
 }
 
-static bool try_to_unmap_hugetlb_one(struct folio *folio,
+static bool try_to_unmap_poisoned_hugetlb_one(struct folio *folio,
 		struct vm_area_struct *vma, unsigned long address, void *arg)
 {
 	DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);

@@ -1993,7 +1993,7 @@ static bool try_to_unmap_hugetlb_one(str
 	 * The try_to_unmap() is only passed a hugetlb folio in the case
 	 * where the hugetlb folio is poisoned.
 	 */
-	VM_WARN_ON_FOLIO(!folio_test_hwpoison(folio), folio);
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_hwpoison(folio), folio);
 	VM_WARN_ON_ONCE(!(flags & TTU_HWPOISON));
 
 	range.end = vma_address_end(&pvmw);

@@ -2031,7 +2031,7 @@ static bool try_to_unmap_hugetlb_one(str
 	if (!folio_test_anon(folio)) {
 		struct mmu_gather tlb;
 
-		VM_WARN_ON(!(flags & TTU_RMAP_LOCKED));
+		VM_WARN_ON_ONCE(!(flags & TTU_RMAP_LOCKED));
 		if (!hugetlb_vma_trylock_write(vma)) {
 			ret = false;
 			goto walk_done;

@@ -2350,7 +2350,7 @@ static bool try_to_unmap_one(struct foli
 		/* Update high watermark before we lower rss */
 		update_hiwater_rss(mm);
 
-		/* With TTU_HWPOISON, we only expect small folios here. */
+		/* unmap_poisoned_folio() only refs order-0 folios */
 		if (folio_test_hwpoison(folio) && (flags & TTU_HWPOISON)) {
 			pteval = swp_entry_to_pte(make_hwpoison_entry(page));
 			dec_mm_counter(mm, mm_counter(folio));

@@ -2440,7 +2440,7 @@ void try_to_unmap(struct folio *folio, e
 {
 	struct rmap_walk_control rwc = {
 		.rmap_one = folio_test_hugetlb(folio) ?
-				try_to_unmap_hugetlb_one : try_to_unmap_one,
+				try_to_unmap_poisoned_hugetlb_one : try_to_unmap_one,
 		.arg = (void *)flags,
 		.done = folio_not_mapped,
 		.anon_lock = folio_lock_anon_vma_read,

_