tree 54a9262ca37905600872eb8638d5453a82f59520
parent 2bb4cd5cc472b191a46938becb7dafdd44644329
author Jens Axboe <axboe@fb.com> 1437059666 -0600
committer Jens Axboe <axboe@fb.com> 1437144113 -0600

block: make /sys/block/<dev>/queue/discard_max_bytes writeable

Lots of devices support huge discard sizes these days. Depending
on how the device handles them internally, huge discards can
introduce massive latencies (hundreds of msec) on the device side.

We have a sysfs file, discard_max_bytes, that advertises the max
hardware supported discard size. Make this writeable, and split
the settings into a soft and hard limit. This can be set from
'discard_granularity' and up to the hardware limit.

Add a new sysfs file, 'discard_max_hw_bytes', that shows the hw
set limit.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>