zram: use notify_free to account all free notifications

`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@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index b13dc993291f..a6148eaf91e5 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@vflare.org>
 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