[PATCH v1 03/18] mm/rmap: add fast-path for small folios when adding/removing/duplicating

David Hildenbrand
2024-04-09T19:24:17Z

Let's add a fast-path for small folios to all relevant rmap functions.
Note that only RMAP_LEVEL_PTE applies.

This is a preparation for tracking the mapcount of large folios in a
single value.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/rmap.h | 13 +++++++++++++
mm/rmap.c | 26 ++++++++++++++++----------
2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 9549d78928bb..327f1ca5a487 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -322,6 +322,11 @@ static __always_inline void __folio_dup_file_rmap(struct folio *folio,

switch (level) {
case RMAP_LEVEL_PTE:
+ if (!folio_test_large(folio)) {
+ atomic_inc(&page->_mapcount);
+ break;
+ }
+
do {
atomic_inc(&page->_mapcount);
} while (page++, --nr_pages > 0);
@@ -405,6 +410,14 @@ static __always_inline int __folio_try_dup_anon_rmap(struct folio *folio,
if (PageAnonExclusive(page + i))
return -EBUSY;
}
+
+ if (!folio_test_large(folio)) {
+ if (PageAnonExclusive(page))
+ ClearPageAnonExclusive(page);
+ atomic_inc(&page->_mapcount);
+ break;
+ }
+
do {
if (PageAnonExclusive(page))
ClearPageAnonExclusive(page);
diff --git a/mm/rmap.c b/mm/rmap.c
index 56b313aa2ebf..4bde6d60db6c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1172,15 +1172,18 @@ static __always_inline unsigned int __folio_add_rmap(struct folio *folio,

switch (level) {
case RMAP_LEVEL_PTE:
+ if (!folio_test_large(folio)) {
+ nr = atomic_inc_and_test(&page->_mapcount);
+ break;
+ }
+
do {
first = atomic_inc_and_test(&page->_mapcount);
- if (first && folio_test_large(folio)) {
+ if (first) {
first = atomic_inc_return_relaxed(mapped);
- first = (first < ENTIRELY_MAPPED);
+ if (first < ENTIRELY_MAPPED)
+ nr++;
}
-
- if (first)
- nr++;
} while (page++, --nr_pages > 0);
break;
case RMAP_LEVEL_PMD:
@@ -1514,15 +1517,18 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,

switch (level) {
case RMAP_LEVEL_PTE:
+ if (!folio_test_large(folio)) {
+ nr = atomic_add_negative(-1, &page->_mapcount);
+ break;
+ }
+
do {
last = atomic_add_negative(-1, &page->_mapcount);
- if (last && folio_test_large(folio)) {
+ if (last) {
last = atomic_dec_return_relaxed(mapped);
- last = (last < ENTIRELY_MAPPED);
+ if (last < ENTIRELY_MAPPED)
+ nr++;
}
-
- if (last)
- nr++;
} while (page++, --nr_pages > 0);
break;
case RMAP_LEVEL_PMD:
--
2.44.0