[PATCH v3 09/20] mm/rmap: abstract large mapcount operations for large folios (!hugetlb)

David Hildenbrand
2025-03-03T16:31:01Z

Let's abstract the operations so we can extend these operations easily.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/rmap.h | 32 ++++++++++++++++++++++++++++----
mm/rmap.c | 14 ++++++--------
2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index e795610bade80..d1e888cc97a58 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -173,6 +173,30 @@ static inline void anon_vma_merge(struct vm_area_struct *vma,

struct anon_vma *folio_get_anon_vma(const struct folio *folio);

+static inline void folio_set_large_mapcount(struct folio *folio, int mapcount,
+ struct vm_area_struct *vma)
+{
+ /* Note: mapcounts start at -1. */
+ atomic_set(&folio->_large_mapcount, mapcount - 1);
+}
+
+static inline void folio_add_large_mapcount(struct folio *folio,
+ int diff, struct vm_area_struct *vma)
+{
+ atomic_add(diff, &folio->_large_mapcount);
+}
+
+static inline void folio_sub_large_mapcount(struct folio *folio,
+ int diff, struct vm_area_struct *vma)
+{
+ atomic_sub(diff, &folio->_large_mapcount);
+}
+
+#define folio_inc_large_mapcount(folio, vma) \
+ folio_add_large_mapcount(folio, 1, vma)
+#define folio_dec_large_mapcount(folio, vma) \
+ folio_sub_large_mapcount(folio, 1, vma)
+
/* RMAP flags, currently only relevant for some anon rmap operations. */
typedef int __bitwise rmap_t;

@@ -352,12 +376,12 @@ static __always_inline void __folio_dup_file_rmap(struct folio *folio,
do {
atomic_inc(&page->_mapcount);
} while (page++, --nr_pages > 0);
- atomic_add(orig_nr_pages, &folio->_large_mapcount);
+ folio_add_large_mapcount(folio, orig_nr_pages, dst_vma);
break;
case RMAP_LEVEL_PMD:
case RMAP_LEVEL_PUD:
atomic_inc(&folio->_entire_mapcount);
- atomic_inc(&folio->_large_mapcount);
+ folio_inc_large_mapcount(folio, dst_vma);
break;
}
}
@@ -451,7 +475,7 @@ static __always_inline int __folio_try_dup_anon_rmap(struct folio *folio,
ClearPageAnonExclusive(page);
atomic_inc(&page->_mapcount);
} while (page++, --nr_pages > 0);
- atomic_add(orig_nr_pages, &folio->_large_mapcount);
+ folio_add_large_mapcount(folio, orig_nr_pages, dst_vma);
break;
case RMAP_LEVEL_PMD:
case RMAP_LEVEL_PUD:
@@ -461,7 +485,7 @@ static __always_inline int __folio_try_dup_anon_rmap(struct folio *folio,
ClearPageAnonExclusive(page);
}
atomic_inc(&folio->_entire_mapcount);
- atomic_inc(&folio->_large_mapcount);
+ folio_inc_large_mapcount(folio, dst_vma);
break;
}
return 0;
diff --git a/mm/rmap.c b/mm/rmap.c
index 8a7d023b02e0c..08846b7eced60 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1266,7 +1266,7 @@ static __always_inline unsigned int __folio_add_rmap(struct folio *folio,
atomic_add_return_relaxed(first, mapped) < ENTIRELY_MAPPED)
nr = first;

- atomic_add(orig_nr_pages, &folio->_large_mapcount);
+ folio_add_large_mapcount(folio, orig_nr_pages, vma);
break;
case RMAP_LEVEL_PMD:
case RMAP_LEVEL_PUD:
@@ -1290,7 +1290,7 @@ static __always_inline unsigned int __folio_add_rmap(struct folio *folio,
nr = 0;
}
}
- atomic_inc(&folio->_large_mapcount);
+ folio_inc_large_mapcount(folio, vma);
break;
}
return nr;
@@ -1556,14 +1556,12 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
SetPageAnonExclusive(page);
}

- /* increment count (starts at -1) */
- atomic_set(&folio->_large_mapcount, nr - 1);
+ folio_set_large_mapcount(folio, nr, vma);
atomic_set(&folio->_nr_pages_mapped, nr);
} else {
/* increment count (starts at -1) */
atomic_set(&folio->_entire_mapcount, 0);
- /* increment count (starts at -1) */
- atomic_set(&folio->_large_mapcount, 0);
+ folio_set_large_mapcount(folio, 1, vma);
atomic_set(&folio->_nr_pages_mapped, ENTIRELY_MAPPED);
if (exclusive)
SetPageAnonExclusive(&folio->page);
@@ -1665,7 +1663,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
break;
}

- atomic_sub(nr_pages, &folio->_large_mapcount);
+ folio_sub_large_mapcount(folio, nr_pages, vma);
do {
last += atomic_add_negative(-1, &page->_mapcount);
} while (page++, --nr_pages > 0);
@@ -1678,7 +1676,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
break;
case RMAP_LEVEL_PMD:
case RMAP_LEVEL_PUD:
- atomic_dec(&folio->_large_mapcount);
+ folio_dec_large_mapcount(folio, vma);
last = atomic_add_negative(-1, &folio->_entire_mapcount);
if (last) {
nr = atomic_sub_return_relaxed(ENTIRELY_MAPPED, mapped);
--
2.48.1