[PATCH RFC 38/39] mm: convert page_try_share_anon_rmap() to folio_try_share_anon_rmap_[pte|pmd]()

[David Hildenbrand]

Let's convert it like we converted all the other rmap functions.
Don't introduce folio_try_share_anon_rmap_ptes() for now, as we don't
have a user that wants rmap batching in sight. Pretty easy to add later.

All users are easy to convert -- only ksm.c doesn't use folios yet but
that is left for future work -- so let's just do it in a single shot.

While at it, turn the BUG_ON into a WARN_ON_ONCE.

Note that page_try_share_anon_rmap() so far didn't care about pte/pmd
mappings (no compound parameter). We're changing that so we can perform
better sanity checks and make the code actually more readable/consistent.
For example, __folio_rmap_sanity_checks() will make sure that a PMD
range actually falls completely into the folio.

Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 include/linux/rmap.h | 98 ++++++++++++++++++++++++++++++++------------
 mm/gup.c             |  2 +-
 mm/huge_memory.c     |  9 ++--
 mm/internal.h        |  4 +-
 mm/ksm.c             |  5 ++-
 mm/migrate_device.c  |  2 +-
 mm/rmap.c            |  9 ++--
 7 files changed, 89 insertions(+), 40 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 3c1df8e020188..ab3ea4583d502 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -267,14 +267,14 @@ static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
 	return 0;
 }
 
-/* See page_try_share_anon_rmap() */
+/* See folio_try_share_anon_rmap_*() */
 static inline int hugetlb_try_share_anon_rmap(struct folio *folio)
 {
 	VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
 	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
 	VM_WARN_ON_FOLIO(!PageAnonExclusive(&folio->page), folio);
 
-	/* See page_try_share_anon_rmap() */
+	/* See folio_try_share_anon_rmap_*() */
 	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
 		smp_mb();
 
@@ -282,7 +282,7 @@ static inline int hugetlb_try_share_anon_rmap(struct folio *folio)
 		return -EBUSY;
 	ClearPageAnonExclusive(&folio->page);
 
-	/* See page_try_share_anon_rmap() */
+	/* See folio_try_share_anon_rmap_*() */
 	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
 		smp_mb__after_atomic();
 	return 0;
@@ -463,30 +463,15 @@ static inline int folio_try_dup_anon_rmap_pmd(struct folio *folio,
 #endif
 }
 
-/**
- * page_try_share_anon_rmap - try marking an exclusive anonymous page possibly
- *			      shared to prepare for KSM or temporary unmapping
- * @page: the exclusive anonymous page to try marking possibly shared
- *
- * The caller needs to hold the PT lock and has to have the page table entry
- * cleared/invalidated.
- *
- * This is similar to folio_try_dup_anon_rmap_*(), however, not used during
- * fork() to duplicate a mapping, but instead to prepare for KSM or temporarily
- * unmapping a page (swap, migration) via folio_remove_rmap_*().
- *
- * Marking the page shared can only fail if the page may be pinned; device
- * private pages cannot get pinned and consequently this function cannot fail.
- *
- * Returns 0 if marking the page possibly shared succeeded. Returns -EBUSY
- * otherwise.
- */
-static inline int page_try_share_anon_rmap(struct page *page)
+static inline int __folio_try_share_anon_rmap(struct folio *folio,
+		struct page *page, unsigned int nr_pages, enum rmap_mode mode)
 {
-	VM_BUG_ON_PAGE(!PageAnon(page) || !PageAnonExclusive(page), page);
+	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+	VM_WARN_ON_FOLIO(!PageAnonExclusive(page), folio);
+	__folio_rmap_sanity_checks(folio, page, nr_pages, mode);
 
-	/* device private pages cannot get pinned via GUP. */
-	if (unlikely(is_device_private_page(page))) {
+	/* device private folios cannot get pinned via GUP. */
+	if (unlikely(folio_is_device_private(folio))) {
 		ClearPageAnonExclusive(page);
 		return 0;
 	}
@@ -537,7 +522,7 @@ static inline int page_try_share_anon_rmap(struct page *page)
 	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
 		smp_mb();
 
-	if (unlikely(page_maybe_dma_pinned(page)))
+	if (unlikely(folio_maybe_dma_pinned(folio)))
 		return -EBUSY;
 	ClearPageAnonExclusive(page);
 
@@ -550,6 +535,67 @@ static inline int page_try_share_anon_rmap(struct page *page)
 	return 0;
 }
 
+/**
+ * folio_try_share_anon_rmap_pte - try marking an exclusive anonymous page
+ *				   mapped by a PTE possibly shared to prepare
+ *				   for KSM or temporary unmapping
+ * @folio:	The folio to share a mapping of
+ * @page:	The mapped exclusive page
+ *
+ * The caller needs to hold the page table lock and has to have the page table
+ * entries cleared/invalidated.
+ *
+ * This is similar to folio_try_dup_anon_rmap_pte(), however, not used during
+ * fork() to duplicate mappings, but instead to prepare for KSM or temporarily
+ * unmapping parts of a folio (swap, migration) via folio_remove_rmap_pte().
+ *
+ * Marking the mapped page shared can only fail if the folio maybe pinned;
+ * device private folios cannot get pinned and consequently this function cannot
+ * fail.
+ *
+ * Returns 0 if marking the mapped page possibly shared succeeded. Returns
+ * -EBUSY otherwise.
+ */
+static inline int folio_try_share_anon_rmap_pte(struct folio *folio,
+		struct page *page)
+{
+	return __folio_try_share_anon_rmap(folio, page, 1, RMAP_MODE_PTE);
+}
+
+/**
+ * folio_try_share_anon_rmap_pmd - try marking an exclusive anonymous page
+ *				   range mapped by a PMD possibly shared to
+ *				   prepare for temporary unmapping
+ * @folio:	The folio to share the mapping of
+ * @page:	The first page to share the mapping of
+ *
+ * The page range of the folio is defined by [page, page + HPAGE_PMD_NR)
+ *
+ * The caller needs to hold the page table lock and has to have the page table
+ * entries cleared/invalidated.
+ *
+ * This is similar to folio_try_dup_anon_rmap_pmd(), however, not used during
+ * fork() to duplicate a mapping, but instead to prepare for temporarily
+ * unmapping parts of a folio (swap, migration) via folio_remove_rmap_pmd().
+ *
+ * Marking the mapped pages shared can only fail if the folio maybe pinned;
+ * device private folios cannot get pinned and consequently this function cannot
+ * fail.
+ *
+ * Returns 0 if marking the mapped pages possibly shared succeeded. Returns
+ * -EBUSY otherwise.
+ */
+static inline int folio_try_share_anon_rmap_pmd(struct folio *folio,
+		struct page *page)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	return __folio_try_share_anon_rmap(folio, page, HPAGE_PMD_NR,
+					 RMAP_MODE_PMD);
+#else
+	WARN_ON_ONCE(true);
+#endif
+}
+
 /*
  * Called from mm/vmscan.c to handle paging out
  */
diff --git a/mm/gup.c b/mm/gup.c
index 231711efa390d..49f32411c68da 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -177,7 +177,7 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
 	/*
 	 * Adjust the pincount before re-checking the PTE for changes.
 	 * This is essentially a smp_mb() and is paired with a memory
-	 * barrier in page_try_share_anon_rmap().
+	 * barrier in folio_try_share_anon_rmap_*().
 	 */
 	smp_mb__after_atomic();
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 138e1e62790be..ebbf5ee6192e7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2224,10 +2224,11 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 		 * In case we cannot clear PageAnonExclusive(), split the PMD
 		 * only and let try_to_migrate_one() fail later.
 		 *
-		 * See page_try_share_anon_rmap(): invalidate PMD first.
+		 * See folio_try_share_anon_rmap_pmd(): invalidate PMD first.
 		 */
 		anon_exclusive = PageAnonExclusive(page);
-		if (freeze && anon_exclusive && page_try_share_anon_rmap(page))
+		if (freeze && anon_exclusive &&
+		    folio_try_share_anon_rmap_pmd(folio, page))
 			freeze = false;
 		if (!freeze) {
 			rmap_t rmap_flags = RMAP_NONE;
@@ -3253,9 +3254,9 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
 	flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
 	pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
 
-	/* See page_try_share_anon_rmap(): invalidate PMD first. */
+	/* See folio_try_share_anon_rmap_pmd(): invalidate PMD first. */
 	anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(page);
-	if (anon_exclusive && page_try_share_anon_rmap(page)) {
+	if (anon_exclusive && folio_try_share_anon_rmap_pmd(folio, page)) {
 		set_pmd_at(mm, address, pvmw->pmd, pmdval);
 		return -EBUSY;
 	}
diff --git a/mm/internal.h b/mm/internal.h
index 43dca750c5afc..b9b630717b9b2 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1047,7 +1047,7 @@ enum {
  * * Ordinary GUP: Using the PT lock
  * * GUP-fast and fork(): mm->write_protect_seq
  * * GUP-fast and KSM or temporary unmapping (swap, migration): see
- *    page_try_share_anon_rmap()
+ *    folio_try_share_anon_rmap_*()
  *
  * Must be called with the (sub)page that's actually referenced via the
  * page table entry, which might not necessarily be the head page for a
@@ -1090,7 +1090,7 @@ static inline bool gup_must_unshare(struct vm_area_struct *vma,
 		return is_cow_mapping(vma->vm_flags);
 	}
 
-	/* Paired with a memory barrier in page_try_share_anon_rmap(). */
+	/* Paired with a memory barrier in folio_try_share_anon_rmap_*(). */
 	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
 		smp_rmb();
 
diff --git a/mm/ksm.c b/mm/ksm.c
index c23aed4f1a344..51f2d989be2be 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1161,8 +1161,9 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 			goto out_unlock;
 		}
 
-		/* See page_try_share_anon_rmap(): clear PTE first. */
-		if (anon_exclusive && page_try_share_anon_rmap(page)) {
+		/* See folio_try_share_anon_rmap_pte(): clear PTE first. */
+		if (anon_exclusive &&
+		    folio_try_share_anon_rmap_pte(page_folio(page), page)) {
 			set_pte_at(mm, pvmw.address, pvmw.pte, entry);
 			goto out_unlock;
 		}
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index c51c99151ebb5..9d0c1ad737225 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -202,7 +202,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			if (anon_exclusive) {
 				pte = ptep_clear_flush(vma, addr, ptep);
 
-				if (page_try_share_anon_rmap(page)) {
+				if (folio_try_share_anon_rmap_pte(folio, page)) {
 					set_pte_at(mm, addr, ptep, pte);
 					folio_unlock(folio);
 					folio_put(folio);
diff --git a/mm/rmap.c b/mm/rmap.c
index 8e86024953c03..7bb3a174efc8d 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1817,9 +1817,9 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 				break;
 			}
 
-			/* See page_try_share_anon_rmap(): clear PTE first. */
+			/* See folio_try_share_anon_rmap(): clear PTE first. */
 			if (anon_exclusive &&
-			    page_try_share_anon_rmap(subpage)) {
+			    folio_try_share_anon_rmap_pte(folio, subpage)) {
 				swap_free(entry);
 				set_pte_at(mm, address, pvmw.pte, pteval);
 				ret = false;
@@ -2093,7 +2093,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 			pte_t swp_pte;
 
 			if (anon_exclusive)
-				BUG_ON(page_try_share_anon_rmap(subpage));
+				WARN_ON_ONCE(folio_try_share_anon_rmap_pte(folio,
+									   subpage));
 
 			/*
 			 * Store the pfn of the page in a special migration
@@ -2175,7 +2176,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 					break;
 				}
 			} else if (anon_exclusive &&
-				   page_try_share_anon_rmap(page)) {
+				   folio_try_share_anon_rmap_pte(folio, subpage)) {
 				set_pte_at(mm, address, pvmw.pte, pteval);
 				ret = false;
 				page_vma_mapped_walk_done(&pvmw);
-- 
2.41.0