block: Track DISCARD statistics and output them in stat and diskstat

Add tracking of REQ_OP_DISCARD ios to the partition statistics and
append them to the various stat files in /sys as well as
/proc/diskstats.  These are tracked with the same four stats as reads
and writes:

Number of discard ios completed.
Number of discard ios merged
Number of discard sectors completed
Milliseconds spent on discard requests

This is done via adding a new STAT_DISCARD define to genhd.h and then
using it to index that stat field for discard requests.

tj: Refreshed on top of v4.17 and other previous updates.

Signed-off-by: Michael Callahan <michaelcallahan@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 10 insertions, 3 deletions

diff --git a/block/genhd.c b/block/genhd.c
index 0711a800d0d4..8cc719a37b32 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1333,8 +1333,11 @@ static int diskstats_show(struct seq_file *seqf, void *v)
                 part_round_stats(gp->queue, cpu, hd);
                 part_stat_unlock();
                 part_in_flight(gp->queue, hd, inflight);
-                seq_printf(seqf, "%4d %7d %s %lu %lu %lu "
-                           "%u %lu %lu %lu %u %u %u %u\n",
+                seq_printf(seqf, "%4d %7d %s "
+                           "%lu %lu %lu %u "
+                           "%lu %lu %lu %u "
+                           "%u %u %u "
+                           "%lu %lu %lu %u\n",
                            MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
                            disk_name(gp, hd->partno, buf),
                            part_stat_read(hd, ios[STAT_READ]),
@@ -1347,7 +1350,11 @@ static int diskstats_show(struct seq_file *seqf, void *v)
                            jiffies_to_msecs(part_stat_read(hd, ticks[STAT_WRITE])),
                            inflight[0],
                            jiffies_to_msecs(part_stat_read(hd, io_ticks)),
-                           jiffies_to_msecs(part_stat_read(hd, time_in_queue))
+                           jiffies_to_msecs(part_stat_read(hd, time_in_queue)),
+                           part_stat_read(hd, ios[STAT_DISCARD]),
+                           part_stat_read(hd, merges[STAT_DISCARD]),
+                           part_stat_read(hd, sectors[STAT_DISCARD]),
+                           jiffies_to_msecs(part_stat_read(hd, ticks[STAT_DISCARD]))
                         );
         }
         disk_part_iter_exit(&piter);