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.

Fixes: be25d1d4e822 ("mm: create new codetag references during page splitting") Signed-off-by: Yu Zhao yuzhao@google.com Acked-by: Suren Baghdasaryan surenb@google.com Cc: stable@vger.kernel.org --- include/linux/mm.h | 30 ++++++++++++++++++++++++++++++ include/linux/pgalloc_tag.h | 31 ------------------------------- mm/huge_memory.c | 2 +- mm/hugetlb.c | 2 +- mm/page_alloc.c | 4 ++-- 5 files changed, 34 insertions(+), 35 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h index b31d4bdd65ad..a07e93adb8ad 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -4137,4 +4137,34 @@ 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 fdc83b0c9e71..2a73efea02d7 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3242,7 +3242,7 @@ 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 2a73753ecf9e..5c77defad295 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3795,7 +3795,7 @@ 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 6b003f57965d..88113fdba956 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2783,7 +2783,7 @@ 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); @@ -4981,7 +4981,7 @@ 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);