The current assumption is that a large folio can only be split into
order-0 folios. That is not the case for hugeTLB demotion, nor for THP
split: see commit c010d47f107f ("mm: thp: split huge page to any lower
order pages").
When a large folio is split into ones of a lower non-zero order, only the
new head pages should be tagged. Tagging tail pages can cause imbalanced
"calls" counters, since only head pages are untagged by pgalloc_tag_sub()
and the "calls" counts on tail pages are leaked, e.g.,
# echo 2048kB >/sys/kernel/mm/hugepages/hugepages-1048576kB/demote_size
# echo 700 >/sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
# time echo 700 >/sys/kernel/mm/hugepages/hugepages-1048576kB/demote
# echo 0 >/sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
# grep alloc_gigantic_folio /proc/allocinfo
Before this patch:
0 549427200 mm/hugetlb.c:1549 func:alloc_gigantic_folio
real 0m2.057s
user 0m0.000s
sys 0m2.051s
After this patch:
0 0 mm/hugetlb.c:1549 func:alloc_gigantic_folio
real 0m1.711s
user 0m0.000s
sys 0m1.704s
Not tagging tail pages also improves the splitting time, e.g., by about
15% when demoting 1GB hugeTLB folios to 2MB ones, as shown above.
Link: https://lkml.kernel.org/r/20240906042108.1150526-2-yuzhao@xxxxxxxxxx
Fixes: be25d1d4e822 ("mm: create new codetag references during page splitting")
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Acked-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b0ff06d18c71..6bb778cbaabf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4084,4 +4084,34 @@ void vma_pgtable_walk_end(struct vm_area_struct *vma);
int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
+#ifdef CONFIG_MEM_ALLOC_PROFILING
+static inline void pgalloc_tag_split(struct folio *folio, int old_order, int new_order)
+{
+ int i;
+ struct alloc_tag *tag;
+ unsigned int nr_pages = 1 << new_order;
+
+ if (!mem_alloc_profiling_enabled())
+ return;
+
+ tag = pgalloc_tag_get(&folio->page);
+ if (!tag)
+ return;
+
+ for (i = nr_pages; i < (1 << old_order); i += nr_pages) {
+ union codetag_ref *ref = get_page_tag_ref(folio_page(folio, i));
+
+ if (ref) {
+ /* Set new reference to point to the original tag */
+ alloc_tag_ref_set(ref, tag);
+ put_page_tag_ref(ref);
+ }
+ }
+}
+#else /* !CONFIG_MEM_ALLOC_PROFILING */
+static inline void pgalloc_tag_split(struct folio *folio, int old_order, int new_order)
+{
+}
+#endif /* CONFIG_MEM_ALLOC_PROFILING */
+
#endif /* _LINUX_MM_H */
diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index 207f0c83c8e9..59a3deb792a8 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -80,36 +80,6 @@ static inline void pgalloc_tag_sub(struct page *page, unsigned int nr)
}
}
-static inline void pgalloc_tag_split(struct page *page, unsigned int nr)
-{
- int i;
- struct page_ext *first_page_ext;
- struct page_ext *page_ext;
- union codetag_ref *ref;
- struct alloc_tag *tag;
-
- if (!mem_alloc_profiling_enabled())
- return;
-
- first_page_ext = page_ext = page_ext_get(page);
- if (unlikely(!page_ext))
- return;
-
- ref = codetag_ref_from_page_ext(page_ext);
- if (!ref->ct)
- goto out;
-
- tag = ct_to_alloc_tag(ref->ct);
- page_ext = page_ext_next(page_ext);
- for (i = 1; i < nr; i++) {
- /* Set new reference to point to the original tag */
- alloc_tag_ref_set(codetag_ref_from_page_ext(page_ext), tag);
- page_ext = page_ext_next(page_ext);
- }
-out:
- page_ext_put(first_page_ext);
-}
-
static inline struct alloc_tag *pgalloc_tag_get(struct page *page)
{
struct alloc_tag *tag = NULL;
@@ -142,7 +112,6 @@ static inline void clear_page_tag_ref(struct page *page) {}
static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
unsigned int nr) {}
static inline void pgalloc_tag_sub(struct page *page, unsigned int nr) {}
-static inline void pgalloc_tag_split(struct page *page, unsigned int nr) {}
static inline struct alloc_tag *pgalloc_tag_get(struct page *page) { return NULL; }
static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr) {}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f15f7faf2a63..cc2872f12030 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3226,7 +3226,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
/* Caller disabled irqs, so they are still disabled here */
split_page_owner(head, order, new_order);
- pgalloc_tag_split(head, 1 << order);
+ pgalloc_tag_split(folio, order, new_order);
/* See comment in __split_huge_page_tail() */
if (folio_test_anon(folio)) {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3faf5aad142d..a8624c07d8bf 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3778,7 +3778,7 @@ static long demote_free_hugetlb_folios(struct hstate *src, struct hstate *dst,
list_del(&folio->lru);
split_page_owner(&folio->page, huge_page_order(src), huge_page_order(dst));
- pgalloc_tag_split(&folio->page, 1 << huge_page_order(src));
+ pgalloc_tag_split(folio, huge_page_order(src), huge_page_order(dst));
for (i = 0; i < pages_per_huge_page(src); i += pages_per_huge_page(dst)) {
struct page *page = folio_page(folio, i);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 74f13f676985..874e006f3d1c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2776,7 +2776,7 @@ void split_page(struct page *page, unsigned int order)
for (i = 1; i < (1 << order); i++)
set_page_refcounted(page + i);
split_page_owner(page, order, 0);
- pgalloc_tag_split(page, 1 << order);
+ pgalloc_tag_split(page_folio(page), order, 0);
split_page_memcg(page, order, 0);
}
EXPORT_SYMBOL_GPL(split_page);
@@ -4974,7 +4974,7 @@ static void *make_alloc_exact(unsigned long addr, unsigned int order,
struct page *last = page + nr;
split_page_owner(page, order, 0);
- pgalloc_tag_split(page, 1 << order);
+ pgalloc_tag_split(page_folio(page), order, 0);
split_page_memcg(page, order, 0);
while (page < --last)
set_page_refcounted(last);
