[HMM 02/16] mm/put_page: move ref decrement to put_zone_device_page()

[JÃrÃme Glisse]

This does not affect non ZONE_DEVICE page. In order to allow
ZONE_DEVICE page to be tracked we need to detect when refcount
of a ZONE_DEVICE page reach 1 (not 0 as non ZONE_DEVICE page).

This patch just move put_page_testzero() from put_page() to
put_zone_device_page() and only for ZONE_DEVICE. It does not
add any overhead compare to existing code.

Signed-off-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
 include/linux/mm.h | 8 +++++---
 kernel/memremap.c  | 2 ++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5f01c88..28e8b28 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -793,11 +793,13 @@ static inline void put_page(struct page *page)
 {
 	page = compound_head(page);
 
+	if (unlikely(is_zone_device_page(page))) {
+		put_zone_device_page(page);
+		return;
+	}
+
 	if (put_page_testzero(page))
 		__put_page(page);
-
-	if (unlikely(is_zone_device_page(page)))
-		put_zone_device_page(page);
 }
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 40d4af8..c821946 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -190,6 +190,8 @@ EXPORT_SYMBOL(get_zone_device_page);
 
 void put_zone_device_page(struct page *page)
 {
+	page_ref_dec(page);
+
 	put_dev_pagemap(page->pgmap);
 }
 EXPORT_SYMBOL(put_zone_device_page);
-- 
2.4.11