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| author | Jens Axboe <axboe@fb.com> | 2015-07-16 09:14:26 -0600 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2015-07-17 08:41:53 -0600 |
| commit | 0034af036554c39eefd14d835a8ec3496ac46712 (patch) | |
| tree | 54a9262ca37905600872eb8638d5453a82f59520 /Documentation/block/queue-sysfs.txt | |
| parent | 2bb4cd5cc472b191a46938becb7dafdd44644329 (diff) | |
| download | lwn-0034af036554c39eefd14d835a8ec3496ac46712.tar.gz lwn-0034af036554c39eefd14d835a8ec3496ac46712.zip | |
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>
Diffstat (limited to 'Documentation/block/queue-sysfs.txt')
| -rw-r--r-- | Documentation/block/queue-sysfs.txt | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt index 3a29f8914df9..e5d914845be6 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_hw_bytes (RO) ---------------------- Devices that support discard functionality may have internal limits on the number of bytes that can be trimmed or unmapped in a single operation. @@ -29,6 +29,14 @@ 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. +discard_max_bytes (RW) +---------------------- +While discard_max_hw_bytes is the hardware limit for the device, this +setting is the software limit. Some devices exhibit large latencies when +large discards are issued, setting this value lower will make Linux issue +smaller discards and potentially help reduce latencies induced by large +discard operations. + discard_zeroes_data (RO) ------------------------ When read, this file will show if the discarded block are zeroed by the |