On 07/14/2015 09:23 AM, Mike Snitzer wrote:
On Tue, Jul 14 2015 at 11:02am -0400,
Jens Axboe <[email protected]> wrote:
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.
Looks pretty good, but we'll lose the original discard_max_bytes once it
is changed. That information loss will prevent users from knowing what
adjustments are possible over time.
This may be OK, but figured i'd raise it.
That's true, I should have mentioned that. But if you write a higher
value than the device supports, then it will be truncated to the max
value that the device supports. So it's not really lost, and it was the
best alternative I could think of.
--
Jens Axboe
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