[PATCH v6 20/37] mm: fix non-compound multi-order memory accounting in __free_pages

[Suren Baghdasaryan]

When a non-compound multi-order page is freed, it is possible that a
speculative reference keeps the page pinned. In this case we free all
pages except for the first page, which will be freed later by the last
put_page(). However the page passed to put_page() is indistinguishable
from an order-0 page, so it cannot do the accounting, just as it cannot
free the subsequent pages.  Do the accounting here, where we free the
pages.

Reported-by: Vlastimil Babka <vba...@suse.cz>
Signed-off-by: Suren Baghdasaryan <sur...@google.com>
---
 include/linux/pgalloc_tag.h | 24 ++++++++++++++++++++++++
 mm/page_alloc.c             |  5 ++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index 093edf98c3d7..50d212330bbb 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -96,12 +96,36 @@ static inline void pgalloc_tag_split(struct page *page, 
unsigned int nr)
        page_ext_put(page_ext);
 }
 
+static inline struct alloc_tag *pgalloc_tag_get(struct page *page)
+{
+       struct alloc_tag *tag = NULL;
+
+       if (mem_alloc_profiling_enabled()) {
+               union codetag_ref *ref = get_page_tag_ref(page);
+
+               alloc_tag_sub_check(ref);
+               if (ref && ref->ct)
+                       tag = ct_to_alloc_tag(ref->ct);
+               put_page_tag_ref(ref);
+       }
+
+       return tag;
+}
+
+static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int 
nr)
+{
+       if (mem_alloc_profiling_enabled() && tag)
+               this_cpu_sub(tag->counters->bytes, PAGE_SIZE * nr);
+}
+
 #else /* CONFIG_MEM_ALLOC_PROFILING */
 
 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) {}
 
 #endif /* CONFIG_MEM_ALLOC_PROFILING */
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fd1cc5b80a56..00e0ae4cbf2d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4700,12 +4700,15 @@ void __free_pages(struct page *page, unsigned int order)
 {
        /* get PageHead before we drop reference */
        int head = PageHead(page);
+       struct alloc_tag *tag = pgalloc_tag_get(page);
 
        if (put_page_testzero(page))
                free_the_page(page, order);
-       else if (!head)
+       else if (!head) {
+               pgalloc_tag_sub_pages(tag, (1 << order) - 1);
                while (order-- > 0)
                        free_the_page(page + (1 << order), order);
+       }
 }
 EXPORT_SYMBOL(__free_pages);
 
-- 
2.44.0.291.gc1ea87d7ee-goog