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87760e5eef
Enable throttling of buffered writeback to make it a lot more smooth, and has way less impact on other system activity. Background writeback should be, by definition, background activity. The fact that we flush huge bundles of it at the time means that it potentially has heavy impacts on foreground workloads, which isn't ideal. We can't easily limit the sizes of writes that we do, since that would impact file system layout in the presence of delayed allocation. So just throttle back buffered writeback, unless someone is waiting for it. The algorithm for when to throttle takes its inspiration in the CoDel networking scheduling algorithm. Like CoDel, blk-wb monitors the minimum latencies of requests over a window of time. In that window of time, if the minimum latency of any request exceeds a given target, then a scale count is incremented and the queue depth is shrunk. The next monitoring window is shrunk accordingly. Unlike CoDel, if we hit a window that exhibits good behavior, then we simply increment the scale count and re-calculate the limits for that scale value. This prevents us from oscillating between a close-to-ideal value and max all the time, instead remaining in the windows where we get good behavior. Unlike CoDel, blk-wb allows the scale count to to negative. This happens if we primarily have writes going on. Unlike positive scale counts, this doesn't change the size of the monitoring window. When the heavy writers finish, blk-bw quickly snaps back to it's stable state of a zero scale count. The patch registers a sysfs entry, 'wb_lat_usec'. This sets the latency target to me met. It defaults to 2 msec for non-rotational storage, and 75 msec for rotational storage. Setting this value to '0' disables blk-wb. Generally, a user would not have to touch this setting. We don't enable WBT on devices that are managed with CFQ, and have a non-root block cgroup attached. If we have a proportional share setup on this particular disk, then the wbt throttling will interfere with that. We don't have a strong need for wbt for that case, since we will rely on CFQ doing that for us. Signed-off-by: Jens Axboe <axboe@fb.com>
169 lines
4.9 KiB
Plaintext
169 lines
4.9 KiB
Plaintext
#
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# Block layer core configuration
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#
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menuconfig BLOCK
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bool "Enable the block layer" if EXPERT
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default y
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select SBITMAP
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select SRCU
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help
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Provide block layer support for the kernel.
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Disable this option to remove the block layer support from the
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kernel. This may be useful for embedded devices.
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If this option is disabled:
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- block device files will become unusable
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- some filesystems (such as ext3) will become unavailable.
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Also, SCSI character devices and USB storage will be disabled since
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they make use of various block layer definitions and facilities.
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Say Y here unless you know you really don't want to mount disks and
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suchlike.
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if BLOCK
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config LBDAF
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bool "Support for large (2TB+) block devices and files"
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depends on !64BIT
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default y
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help
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Enable block devices or files of size 2TB and larger.
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This option is required to support the full capacity of large
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(2TB+) block devices, including RAID, disk, Network Block Device,
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Logical Volume Manager (LVM) and loopback.
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This option also enables support for single files larger than
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2TB.
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The ext4 filesystem requires that this feature be enabled in
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order to support filesystems that have the huge_file feature
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enabled. Otherwise, it will refuse to mount in the read-write
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mode any filesystems that use the huge_file feature, which is
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enabled by default by mke2fs.ext4.
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The GFS2 filesystem also requires this feature.
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If unsure, say Y.
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config BLK_DEV_BSG
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bool "Block layer SG support v4"
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default y
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help
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Saying Y here will enable generic SG (SCSI generic) v4 support
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for any block device.
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Unlike SG v3 (aka block/scsi_ioctl.c drivers/scsi/sg.c), SG v4
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can handle complicated SCSI commands: tagged variable length cdbs
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with bidirectional data transfers and generic request/response
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protocols (e.g. Task Management Functions and SMP in Serial
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Attached SCSI).
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This option is required by recent UDEV versions to properly
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access device serial numbers, etc.
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If unsure, say Y.
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config BLK_DEV_BSGLIB
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bool "Block layer SG support v4 helper lib"
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default n
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select BLK_DEV_BSG
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help
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Subsystems will normally enable this if needed. Users will not
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normally need to manually enable this.
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If unsure, say N.
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config BLK_DEV_INTEGRITY
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bool "Block layer data integrity support"
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select CRC_T10DIF if BLK_DEV_INTEGRITY
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---help---
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Some storage devices allow extra information to be
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stored/retrieved to help protect the data. The block layer
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data integrity option provides hooks which can be used by
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filesystems to ensure better data integrity.
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Say yes here if you have a storage device that provides the
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T10/SCSI Data Integrity Field or the T13/ATA External Path
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Protection. If in doubt, say N.
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config BLK_DEV_ZONED
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bool "Zoned block device support"
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---help---
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Block layer zoned block device support. This option enables
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support for ZAC/ZBC host-managed and host-aware zoned block devices.
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Say yes here if you have a ZAC or ZBC storage device.
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config BLK_DEV_THROTTLING
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bool "Block layer bio throttling support"
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depends on BLK_CGROUP=y
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default n
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---help---
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Block layer bio throttling support. It can be used to limit
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the IO rate to a device. IO rate policies are per cgroup and
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one needs to mount and use blkio cgroup controller for creating
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cgroups and specifying per device IO rate policies.
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See Documentation/cgroups/blkio-controller.txt for more information.
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config BLK_CMDLINE_PARSER
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bool "Block device command line partition parser"
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default n
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---help---
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Enabling this option allows you to specify the partition layout from
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the kernel boot args. This is typically of use for embedded devices
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which don't otherwise have any standardized method for listing the
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partitions on a block device.
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See Documentation/block/cmdline-partition.txt for more information.
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config BLK_WBT
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bool "Enable support for block device writeback throttling"
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default n
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---help---
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Enabling this option enables the block layer to throttle buffered
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background writeback from the VM, making it more smooth and having
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less impact on foreground operations. The throttling is done
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dynamically on an algorithm loosely based on CoDel, factoring in
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the realtime performance of the disk.
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config BLK_WBT_SQ
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bool "Single queue writeback throttling"
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default n
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depends on BLK_WBT
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---help---
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Enable writeback throttling by default on legacy single queue devices
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config BLK_WBT_MQ
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bool "Multiqueue writeback throttling"
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default y
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depends on BLK_WBT
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---help---
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Enable writeback throttling by default on multiqueue devices.
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Multiqueue currently doesn't have support for IO scheduling,
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enabling this option is recommended.
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menu "Partition Types"
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source "block/partitions/Kconfig"
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endmenu
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endif # BLOCK
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config BLOCK_COMPAT
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bool
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depends on BLOCK && COMPAT
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default y
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config BLK_MQ_PCI
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bool
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depends on BLOCK && PCI
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default y
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source block/Kconfig.iosched
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