[PATCH v3 2/2] mm/page_alloc: use a single function to free page

[Aaron Lu]

We have multiple places of freeing a page, most of them doing similar
things and a common function can be used to reduce code duplicate.

It also avoids bug fixed in one function but left in another.

Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx>
---
v3: Vlastimil mentioned the possible performance loss by using
    page_ref_sub_and_test(page, 1) for put_page_testzero(page), since
    we aren't sure so be safe by keeping page ref decreasing code as
    is, only move freeing page part to a common function.

 mm/page_alloc.c | 37 ++++++++++++++-----------------------
 1 file changed, 14 insertions(+), 23 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 91a9a6af41a2..431a03aa96f8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4425,16 +4425,19 @@ unsigned long get_zeroed_page(gfp_t gfp_mask)
 }
 EXPORT_SYMBOL(get_zeroed_page);
 
-void __free_pages(struct page *page, unsigned int order)
+static inline void free_the_page(struct page *page, unsigned int order)
 {
-	if (put_page_testzero(page)) {
-		if (order == 0)
-			free_unref_page(page);
-		else
-			__free_pages_ok(page, order);
-	}
+	if (order == 0)
+		free_unref_page(page);
+	else
+		__free_pages_ok(page, order);
 }
 
+void __free_pages(struct page *page, unsigned int order)
+{
+	if (put_page_testzero(page))
+		free_the_page(page, order);
+}
 EXPORT_SYMBOL(__free_pages);
 
 void free_pages(unsigned long addr, unsigned int order)
@@ -4483,14 +4486,8 @@ void __page_frag_cache_drain(struct page *page, unsigned int count)
 {
 	VM_BUG_ON_PAGE(page_ref_count(page) == 0, page);
 
-	if (page_ref_sub_and_test(page, count)) {
-		unsigned int order = compound_order(page);
-
-		if (order == 0)
-			free_unref_page(page);
-		else
-			__free_pages_ok(page, order);
-	}
+	if (page_ref_sub_and_test(page, count))
+		free_the_page(page, compound_order(page));
 }
 EXPORT_SYMBOL(__page_frag_cache_drain);
 
@@ -4555,14 +4552,8 @@ void page_frag_free(void *addr)
 {
 	struct page *page = virt_to_head_page(addr);
 
-	if (unlikely(put_page_testzero(page))) {
-		unsigned int order = compound_order(page);
-
-		if (order == 0)
-			free_unref_page(page);
-		else
-			__free_pages_ok(page, order);
-	}
+	if (unlikely(put_page_testzero(page)))
+		free_the_page(page, compound_order(page));
 }
 EXPORT_SYMBOL(page_frag_free);
 
-- 
2.17.2