On Thu, Nov 21, 2019 at 08:56:14AM -0700, Jens Axboe wrote:

On 11/21/19 3:40 AM, Konstantin Khlebnikov wrote:

quoted

Requests that triggers flushing volatile writeback cache to disk (barriers)
have significant effect to overall performance.

Block layer has sophisticated engine for combining several flush requests
into one. But there is no statistics for actual flushes executed by disk.
Requests which trigger flushes usually are barriers - zero-size writes.

This patch adds two iostat counters into /sys/class/block/$dev/stat and
/proc/diskstats - count of completed flush requests and their total time.

This makes sense to me, and the "recent" discard addition already proved
that we're fine extending with more fields. Unless folks object, I'd be
happy to queue this up for 5.5.

Looks like a good addition to /me... :)

--D

-- 
Jens Axboe