A ZONE_DEVICE page that reach a refcount of 1 is free ie no longer
have any user. For device private pages this is important to catch
and thus we need to special case put_page() for this.
Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
include/linux/mm.h | 30 ++++++++++++++++++++++++++++++
kernel/memremap.c | 1 -
2 files changed, 30 insertions(+), 1 deletion(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a825dab..11f7bac 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -23,6 +23,7 @@
#include <linux/page_ext.h>
#include <linux/err.h>
#include <linux/page_ref.h>
+#include <linux/memremap.h>
struct mempolicy;
struct anon_vma;
@@ -795,6 +796,20 @@ static inline bool is_device_private_page(const struct page *page)
return ((page_zonenum(page) == ZONE_DEVICE) &&
(page->pgmap->type == MEMORY_DEVICE_PRIVATE));
}
+
+static inline void put_zone_device_private_page(struct page *page)
+{
+ int count = page_ref_dec_return(page);
+
+ /*
+ * If refcount is 1 then page is freed and refcount is stable as nobody
+ * holds a reference on the page.
+ */
+ if (count == 1)
+ page->pgmap->page_free(page, page->pgmap->data);
+ else if (!count)
+ __put_page(page);
+}
#else
static inline bool is_zone_device_page(const struct page *page)
{
@@ -805,6 +820,10 @@ static inline bool is_device_private_page(const struct page *page)
{
return false;
}
+
+static inline void put_zone_device_private_page(struct page *page)
+{
+}
#endif
static inline void get_page(struct page *page)
@@ -822,6 +841,17 @@ static inline void put_page(struct page *page)
{
page = compound_head(page);
+ /*
+ * For private device pages we need to catch refcount transition from
+ * 2 to 1, when refcount reach one it means the private device page is
+ * free and we need to inform the device driver through callback. See
+ * include/linux/memremap.h and HMM for details.
+ */
+ if (unlikely(is_device_private_page(page))) {
+ put_zone_device_private_page(page);
+ return;
+ }
+
if (put_page_testzero(page))
__put_page(page);
}
diff --git a/kernel/memremap.c b/kernel/memremap.c
index dbdb656..71f6f28 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -11,7 +11,6 @@
* General Public License for more details.
*/
#include <linux/radix-tree.h>
-#include <linux/memremap.h>
#include <linux/device.h>
#include <linux/types.h>
#include <linux/pfn_t.h>
--
2.9.3
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