[PATCHv3] zram: use notify_free to account all free notifications

[Sergey Senozhatsky]

`notify_free' device attribute accounts the number of slot free notifications
and internally represents the number of zram_free_page() calls. Slot free
notifications are sent only when device is used as a swap device, hence
`notify_free' is used only for swap devices. Since f4659d8e620d08 (zram:
support REQ_DISCARD) ZRAM handles yet another one free notification (also
via zram_free_page() call) -- REQ_DISCARD requests, which are sent by a
filesystem, whenever some data blocks are discarded. However, there is no
way to know the number of notifications in the latter case.

Use `notify_free' to account the number of pages freed by zram_bio_discard()
and zram_slot_free_notify(). Depending on usage scenario `notify_free'
represents:
 a) the number of pages freed because of slot free notifications, which is
   equal to the number of swap_slot_free_notify() calls, so there is no
   behaviour change

 b) the number of pages freed because of REQ_DISCARD notifications

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-block-zram | 13 ++++++++-----
 drivers/block/zram/zram_drv.c              |  1 +
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index b13dc99..a6148ea 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -77,11 +77,14 @@ What:		/sys/block/zram<id>/notify_free
 Date:		August 2010
 Contact:	Nitin Gupta <ngupta@xxxxxxxxxx>
 Description:
-		The notify_free file is read-only and specifies the number of
-		swap slot free notifications received by this device. These
-		notifications are sent to a swap block device when a swap slot
-		is freed. This statistic is applicable only when this disk is
-		being used as a swap disk.
+		The notify_free file is read-only. Depending on device usage
+		scenario it may account a) the number of pages freed because
+		of swap slot free notifications or b) the number of pages freed
+		because of REQ_DISCARD requests sent by bio. The former ones
+		are sent to a swap block device when a swap slot is freed, which
+		implies that this disk is being used as a swap disk. The latter
+		ones are sent by filesystem mounted with discard option,
+		whenever some data blocks are getting discarded.
 
 What:		/sys/block/zram<id>/zero_pages
 Date:		August 2010
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index d78b245..3b85016 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -698,6 +698,7 @@ static void zram_bio_discard(struct zram *zram, u32 index,
 		bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
 		zram_free_page(zram, index);
 		bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
+		atomic64_inc(&zram->stats.notify_free);
 		index++;
 		n -= PAGE_SIZE;
 	}
-- 
2.1.0.350.g8b25fe0

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