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

Commit Message

Aaron Lu Nov. 5, 2018, 8:58 a.m. UTC

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 and left in another.

Signed-off-by: Aaron Lu <[e-mail]>
---
 mm/page_alloc.c | 37 +++++++++++++++++--------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

Comments

Dave Hansen Nov. 5, 2018, 4:39 p.m. UTC | #1

On 11/5/18 12:58 AM, Aaron Lu wrote:
> 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 and left in another.

Haha, should have read the next patch. :)

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 91a9a6af41a2..2b330296e92a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4425,9 +4425,17 @@ unsigned long get_zeroed_page(gfp_t gfp_mask)
>  }
>  EXPORT_SYMBOL(get_zeroed_page);
>  
> -void __free_pages(struct page *page, unsigned int order)
> +/*
> + * Free a page by reducing its ref count by @nr.
> + * If its refcount reaches 0, then according to its order:
> + * order0: send to PCP;
> + * high order: directly send to Buddy.
> + */

FWIW, I'm not a fan of comments on the function like this.  Please just
comment the *code* that's doing what you describe.  It's easier to read
and less likely to diverge from the code.

The rest of the patch looks great, though.

Patch

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 91a9a6af41a2..2b330296e92a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4425,9 +4425,17 @@  unsigned long get_zeroed_page(gfp_t gfp_mask)
 }
 EXPORT_SYMBOL(get_zeroed_page);
 
-void __free_pages(struct page *page, unsigned int order)
+/*
+ * Free a page by reducing its ref count by @nr.
+ * If its refcount reaches 0, then according to its order:
+ * order0: send to PCP;
+ * high order: directly send to Buddy.
+ */
+static inline void free_the_page(struct page *page, unsigned int order, int nr)
 {
-	if (put_page_testzero(page)) {
+	VM_BUG_ON_PAGE(page_ref_count(page) == 0, page);
+
+	if (page_ref_sub_and_test(page, nr)) {
 		if (order == 0)
 			free_unref_page(page);
 		else
@@ -4435,6 +4443,11 @@  void __free_pages(struct page *page, unsigned int order)
 	}
 }
 
+void __free_pages(struct page *page, unsigned int order)
+{
+	free_the_page(page, order, 1);
+}
+
 EXPORT_SYMBOL(__free_pages);
 
 void free_pages(unsigned long addr, unsigned int order)
@@ -4481,16 +4494,7 @@  static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
 
 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);
-	}
+	free_the_page(page, compound_order(page), count);
 }
 EXPORT_SYMBOL(__page_frag_cache_drain);
 
@@ -4555,14 +4559,7 @@  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);
-	}
+	free_the_page(page, compound_order(page), 1);
 }
 EXPORT_SYMBOL(page_frag_free);