[PATCH] zram: revive swap_slot_free_notify

[Minchan Kim]

<b430e9d1c6d4> "remove compressed copy from zram in-memory"
applied swap_slot_free_notify call in *end_swap_bio_read* to
remove duplicated memory between zram and memory.

However, with introducing rw_page in zram <8c7f01025f7b>
"zram: implement rw_page operation of zram", it became void
because rw_page doesn't need bio.

This patch restores the function for rw_page.

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 mm/page_io.c | 93 ++++++++++++++++++++++++++++++++----------------------------
 1 file changed, 50 insertions(+), 43 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index ff74e512f029..18aac7819cc9 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -66,6 +66,54 @@ void end_swap_bio_write(struct bio *bio)
 	bio_put(bio);
 }
 
+static void swap_slot_free_notify(struct page *page)
+{
+	struct swap_info_struct *sis;
+	struct gendisk *disk;
+
+	/*
+	 * There is no guarantee that the page is in swap cache - the software
+	 * suspend code (at least) uses end_swap_bio_read() against a non-
+	 * swapcache page.  So we must check PG_swapcache before proceeding with
+	 * this optimization.
+	 */
+	if (unlikely(!PageSwapCache(page)))
+		return;
+
+	sis = page_swap_info(page);
+	if (!(sis->flags & SWP_BLKDEV))
+		return;
+
+	/*
+	 * The swap subsystem performs lazy swap slot freeing,
+	 * expecting that the page will be swapped out again.
+	 * So we can avoid an unnecessary write if the page
+	 * isn't redirtied.
+	 * This is good for real swap storage because we can
+	 * reduce unnecessary I/O and enhance wear-leveling
+	 * if an SSD is used as the as swap device.
+	 * But if in-memory swap device (eg zram) is used,
+	 * this causes a duplicated copy between uncompressed
+	 * data in VM-owned memory and compressed data in
+	 * zram-owned memory.  So let's free zram-owned memory
+	 * and make the VM-owned decompressed page *dirty*,
+	 * so the page should be swapped out somewhere again if
+	 * we again wish to reclaim it.
+	 */
+	disk = sis->bdev->bd_disk;
+	if (disk->fops->swap_slot_free_notify) {
+		swp_entry_t entry;
+		unsigned long offset;
+
+		entry.val = page_private(page);
+		offset = swp_offset(entry);
+
+		SetPageDirty(page);
+		disk->fops->swap_slot_free_notify(sis->bdev,
+				offset);
+	}
+}
+
 static void end_swap_bio_read(struct bio *bio)
 {
 	struct page *page = bio->bi_io_vec[0].bv_page;
@@ -81,49 +129,7 @@ static void end_swap_bio_read(struct bio *bio)
 	}
 
 	SetPageUptodate(page);
-
-	/*
-	 * There is no guarantee that the page is in swap cache - the software
-	 * suspend code (at least) uses end_swap_bio_read() against a non-
-	 * swapcache page.  So we must check PG_swapcache before proceeding with
-	 * this optimization.
-	 */
-	if (likely(PageSwapCache(page))) {
-		struct swap_info_struct *sis;
-
-		sis = page_swap_info(page);
-		if (sis->flags & SWP_BLKDEV) {
-			/*
-			 * The swap subsystem performs lazy swap slot freeing,
-			 * expecting that the page will be swapped out again.
-			 * So we can avoid an unnecessary write if the page
-			 * isn't redirtied.
-			 * This is good for real swap storage because we can
-			 * reduce unnecessary I/O and enhance wear-leveling
-			 * if an SSD is used as the as swap device.
-			 * But if in-memory swap device (eg zram) is used,
-			 * this causes a duplicated copy between uncompressed
-			 * data in VM-owned memory and compressed data in
-			 * zram-owned memory.  So let's free zram-owned memory
-			 * and make the VM-owned decompressed page *dirty*,
-			 * so the page should be swapped out somewhere again if
-			 * we again wish to reclaim it.
-			 */
-			struct gendisk *disk = sis->bdev->bd_disk;
-			if (disk->fops->swap_slot_free_notify) {
-				swp_entry_t entry;
-				unsigned long offset;
-
-				entry.val = page_private(page);
-				offset = swp_offset(entry);
-
-				SetPageDirty(page);
-				disk->fops->swap_slot_free_notify(sis->bdev,
-						offset);
-			}
-		}
-	}
-
+	swap_slot_free_notify(page);
 out:
 	unlock_page(page);
 	bio_put(bio);
@@ -347,6 +353,7 @@ int swap_readpage(struct page *page)
 
 	ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
 	if (!ret) {
+		swap_slot_free_notify(page);
 		count_vm_event(PSWPIN);
 		return 0;
 	}
-- 
1.9.1