path: root/Documentation/block/queue-sysfs.txt
diff options
authorAnton Arapov <>2012-10-29 11:15:37 +0100
committerAnton Arapov <>2012-10-29 11:15:37 +0100
commit7d558cd9c7b18e4b16953265aa0da45e63f3b968 (patch)
tree7135d5a810768c9c619346282ee9cfdf1765e225 /Documentation/block/queue-sysfs.txt
parent985ef6b2108ed28ffd5f6630e1e0fce2e2a775f2 (diff)
fedora kernel: cd394142aac30b5c751f25b517572e2448695641v3.6.3-2f17
Signed-off-by: Anton Arapov <>
Diffstat (limited to 'Documentation/block/queue-sysfs.txt')
1 files changed, 71 insertions, 0 deletions
diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
index d8147b336c3..e54ac1d5340 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -9,20 +9,71 @@ These files are the ones found in the /sys/block/xxx/queue/ directory.
Files denoted with a RO postfix are readonly and the RW postfix means
+add_random (RW)
+This file allows to trun off the disk entropy contribution. Default
+value of this file is '1'(on).
+discard_granularity (RO)
+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)
+Devices that support discard functionality may have internal limits on
+the number of bytes that can be trimmed or unmapped in a single operation.
+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.
+discard_zeroes_data (RO)
+When read, this file will show if the discarded block are zeroed by the
+device or not. If its value is '1' the blocks are zeroed otherwise not.
hw_sector_size (RO)
This is the hardware sector size of the device, in bytes.
+iostats (RW)
+This file is used to control (on/off) the iostats accounting of the
+logical_block_size (RO)
+This is the logcal block size of the device, in bytes.
max_hw_sectors_kb (RO)
This is the maximum number of kilobytes supported in a single data transfer.
+max_integrity_segments (RO)
+When read, this file shows the max limit of integrity segments as
+set by block layer which a hardware controller can handle.
max_sectors_kb (RW)
This is the maximum number of kilobytes that the block layer will allow
for a filesystem request. Must be smaller than or equal to the maximum
size allowed by the hardware.
+max_segments (RO)
+Maximum number of segments of the device.
+max_segment_size (RO)
+Maximum segment size of the device.
+minimum_io_size (RO)
+This is the smallest preferred io size reported by the device.
nomerges (RW)
This enables the user to disable the lookup logic involved with IO
@@ -38,11 +89,31 @@ read or write requests. Note that the total allocated number may be twice
this amount, since it applies only to reads or writes (not the accumulated
+To avoid priority inversion through request starvation, a request
+queue maintains a separate request pool per each cgroup when
+CONFIG_BLK_CGROUP is enabled, and this parameter applies to each such
+per-block-cgroup request pool. IOW, if there are N block cgroups,
+each request queue may have upto N request pools, each independently
+regulated by nr_requests.
+optimal_io_size (RO)
+This is the optimal io size reported by the device.
+physical_block_size (RO)
+This is the physical block size of device, in bytes.
read_ahead_kb (RW)
Maximum number of kilobytes to read-ahead for filesystems on this block
+rotational (RW)
+This file is used to stat if the device is of rotational type or
+non-rotational type.
rq_affinity (RW)
If this option is '1', the block layer will migrate request completions to the