On 07/16/2015 09:07 AM, Jeff Moyer wrote:
Jens Axboe <ax...@fb.com> writes:
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.
Signed-off-by: Jens Axboe <ax...@fb.com>
---
Documentation/block/queue-sysfs.txt | 4 +++-
block/blk-settings.c | 4 ++++
block/blk-sysfs.c | 40 ++++++++++++++++++++++++++++++++++++-
include/linux/blkdev.h | 1 +
4 files changed, 47 insertions(+), 2 deletions(-)
diff --git a/Documentation/block/queue-sysfs.txt
b/Documentation/block/queue-sysfs.txt
index 3a29f8914df9..3748cf827131 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -20,7 +20,7 @@ This shows the size of internal allocation of the device in
bytes, if
reported by the device. A value of '0' means device does not support
the discard functionality.
-discard_max_bytes (RO)
+discard_max_bytes (RW)
----------------------
Devices that support discard functionality may have internal limits on
the number of bytes that can be trimmed or unmapped in a single operation.
@@ -28,6 +28,8 @@ The discard_max_bytes parameter is set by the device driver
to the maximum
number of bytes that can be discarded in a single operation. Discard
requests issued to the device must not exceed this limit. A discard_max_bytes
value of 0 means that the device does not support discard functionality.
+Writing a lower value to this file can limit the maximum discard size issued
+to the device, which can help latencies.
You forgot to add a new entry for discard_max_hw_bytes. Fix that and
you can slap my 'Reviewed-by: Jeff Moyer <jmo...@redhat.com>' on there.
I thought you meant sysfs, so I had to go back and check. But
documentation, yep, I forgot that. I'll add it. Thanks!
--
Jens Axboe
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
