[PATCH WIP v1 01/20] mm/rmap: factor out adding folio range into __folio_add_rmap_range()

[David Hildenbrand]

Let's factor it out, optimize for small folios, and add some more sanity
checks.

Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 mm/rmap.c | 119 ++++++++++++++++++++++++------------------------------
 1 file changed, 53 insertions(+), 66 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 7a27a2b41802..afddf3d82a8f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1127,6 +1127,54 @@ int folio_total_mapcount(struct folio *folio)
 	return mapcount;
 }
 
+static unsigned int __folio_add_rmap_range(struct folio *folio,
+		struct page *page, unsigned int nr_pages, bool compound,
+		int *nr_pmdmapped)
+{
+	atomic_t *mapped = &folio->_nr_pages_mapped;
+	int first, nr = 0;
+
+	VM_WARN_ON_FOLIO(compound && page != &folio->page, folio);
+	VM_WARN_ON_FOLIO(compound && !folio_test_pmd_mappable(folio), folio);
+	VM_WARN_ON_FOLIO(compound && nr_pages != folio_nr_pages(folio), folio);
+	VM_WARN_ON_FOLIO(!folio_test_large(folio) && nr_pages != 1, folio);
+
+	if (likely(!folio_test_large(folio)))
+		return atomic_inc_and_test(&page->_mapcount);
+
+	/* Is page being mapped by PTE? Is this its first map to be added? */
+	if (!compound) {
+		do {
+			first = atomic_inc_and_test(&page->_mapcount);
+			if (first) {
+				first = atomic_inc_return_relaxed(mapped);
+				if (first < COMPOUND_MAPPED)
+					nr++;
+			}
+		} while (page++, --nr_pages > 0);
+	} else if (folio_test_pmd_mappable(folio)) {
+		/* That test is redundant: it's for safety or to optimize out */
+
+		first = atomic_inc_and_test(&folio->_entire_mapcount);
+		if (first) {
+			nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped);
+			if (likely(nr < COMPOUND_MAPPED + COMPOUND_MAPPED)) {
+				*nr_pmdmapped = folio_nr_pages(folio);
+				nr = *nr_pmdmapped - (nr & FOLIO_PAGES_MAPPED);
+				/* Raced ahead of a remove and another add? */
+				if (unlikely(nr < 0))
+					nr = 0;
+			} else {
+				/* Raced ahead of a remove of COMPOUND_MAPPED */
+				nr = 0;
+			}
+		}
+	} else {
+		VM_WARN_ON_ONCE_FOLIO(true, folio);
+	}
+	return nr;
+}
+
 /**
  * folio_move_anon_rmap - move a folio to our anon_vma
  * @folio:	The folio to move to our anon_vma
@@ -1227,38 +1275,10 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
 		unsigned long address, rmap_t flags)
 {
 	struct folio *folio = page_folio(page);
-	atomic_t *mapped = &folio->_nr_pages_mapped;
-	int nr = 0, nr_pmdmapped = 0;
+	unsigned int nr, nr_pmdmapped = 0;
 	bool compound = flags & RMAP_COMPOUND;
-	bool first;
-
-	/* Is page being mapped by PTE? Is this its first map to be added? */
-	if (likely(!compound)) {
-		first = atomic_inc_and_test(&page->_mapcount);
-		nr = first;
-		if (first && folio_test_large(folio)) {
-			nr = atomic_inc_return_relaxed(mapped);
-			nr = (nr < COMPOUND_MAPPED);
-		}
-	} else if (folio_test_pmd_mappable(folio)) {
-		/* That test is redundant: it's for safety or to optimize out */
-
-		first = atomic_inc_and_test(&folio->_entire_mapcount);
-		if (first) {
-			nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped);
-			if (likely(nr < COMPOUND_MAPPED + COMPOUND_MAPPED)) {
-				nr_pmdmapped = folio_nr_pages(folio);
-				nr = nr_pmdmapped - (nr & FOLIO_PAGES_MAPPED);
-				/* Raced ahead of a remove and another add? */
-				if (unlikely(nr < 0))
-					nr = 0;
-			} else {
-				/* Raced ahead of a remove of COMPOUND_MAPPED */
-				nr = 0;
-			}
-		}
-	}
 
+	nr = __folio_add_rmap_range(folio, page, 1, compound, &nr_pmdmapped);
 	if (nr_pmdmapped)
 		__lruvec_stat_mod_folio(folio, NR_ANON_THPS, nr_pmdmapped);
 	if (nr)
@@ -1349,43 +1369,10 @@ void folio_add_file_rmap_range(struct folio *folio, struct page *page,
 			unsigned int nr_pages, struct vm_area_struct *vma,
 			bool compound)
 {
-	atomic_t *mapped = &folio->_nr_pages_mapped;
-	unsigned int nr_pmdmapped = 0, first;
-	int nr = 0;
-
-	VM_WARN_ON_FOLIO(compound && !folio_test_pmd_mappable(folio), folio);
-
-	/* Is page being mapped by PTE? Is this its first map to be added? */
-	if (likely(!compound)) {
-		do {
-			first = atomic_inc_and_test(&page->_mapcount);
-			if (first && folio_test_large(folio)) {
-				first = atomic_inc_return_relaxed(mapped);
-				first = (first < COMPOUND_MAPPED);
-			}
-
-			if (first)
-				nr++;
-		} while (page++, --nr_pages > 0);
-	} else if (folio_test_pmd_mappable(folio)) {
-		/* That test is redundant: it's for safety or to optimize out */
-
-		first = atomic_inc_and_test(&folio->_entire_mapcount);
-		if (first) {
-			nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped);
-			if (likely(nr < COMPOUND_MAPPED + COMPOUND_MAPPED)) {
-				nr_pmdmapped = folio_nr_pages(folio);
-				nr = nr_pmdmapped - (nr & FOLIO_PAGES_MAPPED);
-				/* Raced ahead of a remove and another add? */
-				if (unlikely(nr < 0))
-					nr = 0;
-			} else {
-				/* Raced ahead of a remove of COMPOUND_MAPPED */
-				nr = 0;
-			}
-		}
-	}
+	unsigned int nr, nr_pmdmapped = 0;
 
+	nr = __folio_add_rmap_range(folio, page, nr_pages, compound,
+				    &nr_pmdmapped);
 	if (nr_pmdmapped)
 		__lruvec_stat_mod_folio(folio, folio_test_swapbacked(folio) ?
 			NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);
-- 
2.41.0