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Merge tag 'for-4.16/dm-changes' of git://git.kernel.org/pub/scm/linux…
…/kernel/git/device-mapper/linux-dm Pull device mapper updates from Mike Snitzer: - DM core fixes to ensure that bio submission follows a depth-first tree walk; this is critical to allow forward progress without the need to use the bioset's BIOSET_NEED_RESCUER. - Remove DM core's BIOSET_NEED_RESCUER based dm_offload infrastructure. - DM core cleanups and improvements to make bio-based DM more efficient (e.g. reduced memory footprint as well leveraging per-bio-data more). - Introduce new bio-based mode (DM_TYPE_NVME_BIO_BASED) that leverages the more direct IO submission path in the block layer; this mode is used by DM multipath and also optimizes targets like DM thin-pool that stack directly on NVMe data device. - DM multipath improvements to factor out legacy SCSI-only (e.g. scsi_dh) code paths to allow for more optimized support for NVMe multipath. - A fix for DM multipath path selectors (service-time and queue-length) to select paths in a more balanced way; largely academic but doesn't hurt. - Numerous DM raid target fixes and improvements. - Add a new DM "unstriped" target that enables Intel to workaround firmware limitations in some NVMe drives that are striped internally (this target also works when stacked above the DM "striped" target). - Various Documentation fixes and improvements. - Misc cleanups and fixes across various DM infrastructure and targets (e.g. bufio, flakey, log-writes, snapshot). * tag 'for-4.16/dm-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm: (69 commits) dm cache: Documentation: update default migration_throttling value dm mpath selector: more evenly distribute ties dm unstripe: fix target length versus number of stripes size check dm thin: fix trailing semicolon in __remap_and_issue_shared_cell dm table: fix NVMe bio-based dm_table_determine_type() validation dm: various cleanups to md->queue initialization code dm mpath: delay the retry of a request if the target responded as busy dm mpath: return DM_MAPIO_DELAY_REQUEUE if QUEUE_IO or PG_INIT_REQUIRED dm mpath: return DM_MAPIO_REQUEUE on blk-mq rq allocation failure dm log writes: fix max length used for kstrndup dm: backfill missing calls to mutex_destroy() dm snapshot: use mutex instead of rw_semaphore dm flakey: check for null arg_name in parse_features() dm thin: extend thinpool status format string with omitted fields dm thin: fixes in thin-provisioning.txt dm thin: document representation of <highest mapped sector> when there is none dm thin: fix documentation relative to low water mark threshold dm cache: be consistent in specifying sectors and SI units in cache.txt dm cache: delete obsoleted paragraph in cache.txt dm cache: fix grammar in cache-policies.txt ...
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,124 @@ | ||
| Introduction | ||
| ============ | ||
|
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| The device-mapper "unstriped" target provides a transparent mechanism to | ||
| unstripe a device-mapper "striped" target to access the underlying disks | ||
| without having to touch the true backing block-device. It can also be | ||
| used to unstripe a hardware RAID-0 to access backing disks. | ||
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| Parameters: | ||
| <number of stripes> <chunk size> <stripe #> <dev_path> <offset> | ||
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| <number of stripes> | ||
| The number of stripes in the RAID 0. | ||
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| <chunk size> | ||
| The amount of 512B sectors in the chunk striping. | ||
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| <dev_path> | ||
| The block device you wish to unstripe. | ||
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| <stripe #> | ||
| The stripe number within the device that corresponds to physical | ||
| drive you wish to unstripe. This must be 0 indexed. | ||
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| Why use this module? | ||
| ==================== | ||
|
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| An example of undoing an existing dm-stripe | ||
| ------------------------------------------- | ||
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| This small bash script will setup 4 loop devices and use the existing | ||
| striped target to combine the 4 devices into one. It then will use | ||
| the unstriped target ontop of the striped device to access the | ||
| individual backing loop devices. We write data to the newly exposed | ||
| unstriped devices and verify the data written matches the correct | ||
| underlying device on the striped array. | ||
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| #!/bin/bash | ||
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| MEMBER_SIZE=$((128 * 1024 * 1024)) | ||
| NUM=4 | ||
| SEQ_END=$((${NUM}-1)) | ||
| CHUNK=256 | ||
| BS=4096 | ||
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| RAID_SIZE=$((${MEMBER_SIZE}*${NUM}/512)) | ||
| DM_PARMS="0 ${RAID_SIZE} striped ${NUM} ${CHUNK}" | ||
| COUNT=$((${MEMBER_SIZE} / ${BS})) | ||
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| for i in $(seq 0 ${SEQ_END}); do | ||
| dd if=/dev/zero of=member-${i} bs=${MEMBER_SIZE} count=1 oflag=direct | ||
| losetup /dev/loop${i} member-${i} | ||
| DM_PARMS+=" /dev/loop${i} 0" | ||
| done | ||
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| echo $DM_PARMS | dmsetup create raid0 | ||
| for i in $(seq 0 ${SEQ_END}); do | ||
| echo "0 1 unstriped ${NUM} ${CHUNK} ${i} /dev/mapper/raid0 0" | dmsetup create set-${i} | ||
| done; | ||
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| for i in $(seq 0 ${SEQ_END}); do | ||
| dd if=/dev/urandom of=/dev/mapper/set-${i} bs=${BS} count=${COUNT} oflag=direct | ||
| diff /dev/mapper/set-${i} member-${i} | ||
| done; | ||
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| for i in $(seq 0 ${SEQ_END}); do | ||
| dmsetup remove set-${i} | ||
| done | ||
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| dmsetup remove raid0 | ||
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| for i in $(seq 0 ${SEQ_END}); do | ||
| losetup -d /dev/loop${i} | ||
| rm -f member-${i} | ||
| done | ||
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| Another example | ||
| --------------- | ||
|
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| Intel NVMe drives contain two cores on the physical device. | ||
| Each core of the drive has segregated access to its LBA range. | ||
| The current LBA model has a RAID 0 128k chunk on each core, resulting | ||
| in a 256k stripe across the two cores: | ||
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| Core 0: Core 1: | ||
| __________ __________ | ||
| | LBA 512| | LBA 768| | ||
| | LBA 0 | | LBA 256| | ||
| ---------- ---------- | ||
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| The purpose of this unstriping is to provide better QoS in noisy | ||
| neighbor environments. When two partitions are created on the | ||
| aggregate drive without this unstriping, reads on one partition | ||
| can affect writes on another partition. This is because the partitions | ||
| are striped across the two cores. When we unstripe this hardware RAID 0 | ||
| and make partitions on each new exposed device the two partitions are now | ||
| physically separated. | ||
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| With the dm-unstriped target we're able to segregate an fio script that | ||
| has read and write jobs that are independent of each other. Compared to | ||
| when we run the test on a combined drive with partitions, we were able | ||
| to get a 92% reduction in read latency using this device mapper target. | ||
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| Example dmsetup usage | ||
| ===================== | ||
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| unstriped ontop of Intel NVMe device that has 2 cores | ||
| ----------------------------------------------------- | ||
| dmsetup create nvmset0 --table '0 512 unstriped 2 256 0 /dev/nvme0n1 0' | ||
| dmsetup create nvmset1 --table '0 512 unstriped 2 256 1 /dev/nvme0n1 0' | ||
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| There will now be two devices that expose Intel NVMe core 0 and 1 | ||
| respectively: | ||
| /dev/mapper/nvmset0 | ||
| /dev/mapper/nvmset1 | ||
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| unstriped ontop of striped with 4 drives using 128K chunk size | ||
| -------------------------------------------------------------- | ||
| dmsetup create raid_disk0 --table '0 512 unstriped 4 256 0 /dev/mapper/striped 0' | ||
| dmsetup create raid_disk1 --table '0 512 unstriped 4 256 1 /dev/mapper/striped 0' | ||
| dmsetup create raid_disk2 --table '0 512 unstriped 4 256 2 /dev/mapper/striped 0' | ||
| dmsetup create raid_disk3 --table '0 512 unstriped 4 256 3 /dev/mapper/striped 0' |
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