dm: add unstriped target (18a5bf27) · Commits · 戴 / test

Documentation/device-mapper/unstriped.txt

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		Introduction
		============

		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.

		Parameters:
		<number of stripes> <chunk size> <stripe #> <dev_path> <offset>

		<number of stripes>
		The number of stripes in the RAID 0.

		<chunk size>
		The amount of 512B sectors in the chunk striping.

		<dev_path>
		The block device you wish to unstripe.

		<stripe #>
		The stripe number within the device that corresponds to physical
		drive you wish to unstripe. This must be 0 indexed.


		Why use this module?
		====================

		An example of undoing an existing dm-stripe
		-------------------------------------------

		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.

		#!/bin/bash

		MEMBER_SIZE=$((128 * 1024 * 1024))
		NUM=4
		SEQ_END=$((${NUM}-1))
		CHUNK=256
		BS=4096

		RAID_SIZE=$((${MEMBER_SIZE}*${NUM}/512))
		DM_PARMS="0 ${RAID_SIZE} striped ${NUM} ${CHUNK}"
		COUNT=$((${MEMBER_SIZE} / ${BS}))

		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

		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;

		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;

		for i in $(seq 0 ${SEQ_END}); do
		dmsetup remove set-${i}
		done

		dmsetup remove raid0

		for i in $(seq 0 ${SEQ_END}); do
		losetup -d /dev/loop${i}
		rm -f member-${i}
		done

		Another example
		---------------

		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:

		Core 0: Core 1:
		__________ __________
		\| LBA 512\| \| LBA 768\|
		\| LBA 0 \| \| LBA 256\|
		---------- ----------

		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.

		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.


		Example dmsetup usage
		=====================

		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'

		There will now be two devices that expose Intel NVMe core 0 and 1
		respectively:
		/dev/mapper/nvmset0
		/dev/mapper/nvmset1

		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'

drivers/md/Kconfig

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		@@ -269,6 +269,13 @@ config DM_BIO_PRISON

		source "drivers/md/persistent-data/Kconfig"

		config DM_UNSTRIPED
		tristate "Unstriped target"
		depends on BLK_DEV_DM
		---help---
		Unstripes I/O so it is issued solely on a single drive in a HW
		RAID0 or dm-striped target.

		config DM_CRYPT
		tristate "Crypt target support"
		depends on BLK_DEV_DM

drivers/md/Makefile

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		@@ -43,6 +43,7 @@ obj-$(CONFIG_BCACHE) += bcache/
		obj-$(CONFIG_BLK_DEV_MD) += md-mod.o
		obj-$(CONFIG_BLK_DEV_DM) += dm-mod.o
		obj-$(CONFIG_BLK_DEV_DM_BUILTIN) += dm-builtin.o
		obj-$(CONFIG_DM_UNSTRIPED) += dm-unstripe.o
		obj-$(CONFIG_DM_BUFIO) += dm-bufio.o
		obj-$(CONFIG_DM_BIO_PRISON) += dm-bio-prison.o
		obj-$(CONFIG_DM_CRYPT) += dm-crypt.o

drivers/md/dm-unstripe.c

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		/*
		* Copyright (C) 2017 Intel Corporation.
		*
		* This file is released under the GPL.
		*/

		#include "dm.h"

		#include <linux/module.h>
		#include <linux/init.h>
		#include <linux/blkdev.h>
		#include <linux/bio.h>
		#include <linux/slab.h>
		#include <linux/bitops.h>
		#include <linux/device-mapper.h>

		struct unstripe_c {
		struct dm_dev *dev;
		sector_t physical_start;

		uint32_t stripes;

		uint32_t unstripe;
		sector_t unstripe_width;
		sector_t unstripe_offset;

		uint32_t chunk_size;
		u8 chunk_shift;
		};

		#define DM_MSG_PREFIX "unstriped"

		static void cleanup_unstripe(struct unstripe_c uc, struct dm_target ti)
		{
		if (uc->dev)
		dm_put_device(ti, uc->dev);
		kfree(uc);
		}

		/*
		* Contruct an unstriped mapping.
		* <number of stripes> <chunk size> <stripe #> <dev_path> <offset>
		*/
		static int unstripe_ctr(struct dm_target ti, unsigned int argc, char *argv)
		{
		struct unstripe_c *uc;
		sector_t width, tmp_len;
		unsigned long long start;
		char dummy;

		if (argc != 5) {
		ti->error = "Invalid number of arguments";
		return -EINVAL;
		}

		uc = kzalloc(sizeof(*uc), GFP_KERNEL);
		if (!uc) {
		ti->error = "Memory allocation for unstriped context failed";
		return -ENOMEM;
		}

		if (kstrtouint(argv[0], 10, &uc->stripes) \|\| !uc->stripes) {
		ti->error = "Invalid stripe count";
		goto err;
		}

		if (kstrtouint(argv[1], 10, &uc->chunk_size) \|\| !uc->chunk_size) {
		ti->error = "Invalid chunk_size";
		goto err;
		}

		// FIXME: must support non power of 2 chunk_size, dm-stripe.c does
		if (!is_power_of_2(uc->chunk_size)) {
		ti->error = "Non power of 2 chunk_size is not supported yet";
		goto err;
		}

		if (kstrtouint(argv[2], 10, &uc->unstripe)) {
		ti->error = "Invalid stripe number";
		goto err;
		}

		if (uc->unstripe > uc->stripes && uc->stripes > 1) {
		ti->error = "Please provide stripe between [0, # of stripes]";
		goto err;
		}

		if (dm_get_device(ti, argv[3], dm_table_get_mode(ti->table), &uc->dev)) {
		ti->error = "Couldn't get striped device";
		goto err;
		}

		if (sscanf(argv[4], "%llu%c", &start, &dummy) != 1) {
		ti->error = "Invalid striped device offset";
		goto err;
		}
		uc->physical_start = start;

		uc->unstripe_offset = uc->unstripe * uc->chunk_size;
		uc->unstripe_width = (uc->stripes - 1) * uc->chunk_size;
		uc->chunk_shift = fls(uc->chunk_size) - 1;

		width = ti->len;
		if (sector_div(width, uc->stripes)) {
		ti->error = "Target length not divisible by number of stripes";
		goto err;
		}

		tmp_len = width;
		if (sector_div(tmp_len, uc->chunk_size)) {
		ti->error = "Target length not divisible by chunk size";
		goto err;
		}

		if (dm_set_target_max_io_len(ti, uc->chunk_size)) {
		ti->error = "Failed to set max io len";
		goto err;
		}

		ti->private = uc;
		return 0;
		err:
		cleanup_unstripe(uc, ti);
		return -EINVAL;
		}

		static void unstripe_dtr(struct dm_target *ti)
		{
		struct unstripe_c *uc = ti->private;

		cleanup_unstripe(uc, ti);
		}

		static sector_t map_to_core(struct dm_target ti, struct bio bio)
		{
		struct unstripe_c *uc = ti->private;
		sector_t sector = bio->bi_iter.bi_sector;

		/* Shift us up to the right "row" on the stripe */
		sector += uc->unstripe_width * (sector >> uc->chunk_shift);

		/* Account for what stripe we're operating on */
		sector += uc->unstripe_offset;

		return sector;
		}

		static int unstripe_map(struct dm_target ti, struct bio bio)
		{
		struct unstripe_c *uc = ti->private;

		bio_set_dev(bio, uc->dev->bdev);
		bio->bi_iter.bi_sector = map_to_core(ti, bio) + uc->physical_start;

		return DM_MAPIO_REMAPPED;
		}

		static void unstripe_status(struct dm_target *ti, status_type_t type,
		unsigned int status_flags, char *result, unsigned int maxlen)
		{
		struct unstripe_c *uc = ti->private;
		unsigned int sz = 0;

		switch (type) {
		case STATUSTYPE_INFO:
		break;

		case STATUSTYPE_TABLE:
		DMEMIT("%d %llu %d %s %llu",
		uc->stripes, (unsigned long long)uc->chunk_size, uc->unstripe,
		uc->dev->name, (unsigned long long)uc->physical_start);
		break;
		}
		}

		static int unstripe_iterate_devices(struct dm_target *ti,
		iterate_devices_callout_fn fn, void *data)
		{
		struct unstripe_c *uc = ti->private;

		return fn(ti, uc->dev, uc->physical_start, ti->len, data);
		}

		static void unstripe_io_hints(struct dm_target *ti,
		struct queue_limits *limits)
		{
		struct unstripe_c *uc = ti->private;

		limits->chunk_sectors = uc->chunk_size;
		}

		static struct target_type unstripe_target = {
		.name = "unstriped",
		.version = {1, 0, 0},
		.module = THIS_MODULE,
		.ctr = unstripe_ctr,
		.dtr = unstripe_dtr,
		.map = unstripe_map,
		.status = unstripe_status,
		.iterate_devices = unstripe_iterate_devices,
		.io_hints = unstripe_io_hints,
		};

		static int __init dm_unstripe_init(void)
		{
		int r;

		r = dm_register_target(&unstripe_target);
		if (r < 0)
		DMERR("target registration failed");

		return r;
		}

		static void __exit dm_unstripe_exit(void)
		{
		dm_unregister_target(&unstripe_target);
		}

		module_init(dm_unstripe_init);
		module_exit(dm_unstripe_exit);

		MODULE_DESCRIPTION(DM_NAME " unstriped target");
		MODULE_AUTHOR("Scott Bauer <scott.bauer@intel.com>");
		MODULE_LICENSE("GPL");

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