Commit 9903883f authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'dm-3.11-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/agk/linux-dm 

Pull device-mapper changes from Alasdair G Kergon:
 "Add a device-mapper target called dm-switch to provide a multipath
  framework for storage arrays that dynamically reconfigure their
  preferred paths for different device regions.

  Fix a bug in the verity target that prevented its use with some
  specific sizes of devices.

  Improve some locking mechanisms in the device-mapper core and bufio.

  Add Mike Snitzer as a device-mapper maintainer.

  A few more clean-ups and fixes"

* tag 'dm-3.11-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/agk/linux-dm:
  dm: add switch target
  dm: update maintainers
  dm: optimize reorder structure
  dm: optimize use SRCU and RCU
  dm bufio: submit writes outside lock
  dm cache: fix arm link errors with inline
  dm verity: use __ffs and __fls
  dm flakey: correct ctr alloc failure mesg
  dm verity: remove pointless comparison
  dm: use __GFP_HIGHMEM in __vmalloc
  dm verity: fix inability to use a few specific devices sizes
  dm ioctl: set noio flag to avoid __vmalloc deadlock
  dm mpath: fix ioctl deadlock when no paths
parents 36805aae 9d0eb0ab

Documentation/device-mapper/switch.txt

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+126 −0
Original line number Diff line number Diff line 
dm-switch

=========



The device-mapper switch target creates a device that supports an

arbitrary mapping of fixed-size regions of I/O across a fixed set of

paths.  The path used for any specific region can be switched

dynamically by sending the target a message.



It maps I/O to underlying block devices efficiently when there is a large

number of fixed-sized address regions but there is no simple pattern

that would allow for a compact representation of the mapping such as

dm-stripe.



Background

----------



Dell EqualLogic and some other iSCSI storage arrays use a distributed

frameless architecture.  In this architecture, the storage group

consists of a number of distinct storage arrays ("members") each having

independent controllers, disk storage and network adapters.  When a LUN

is created it is spread across multiple members.  The details of the

spreading are hidden from initiators connected to this storage system.

The storage group exposes a single target discovery portal, no matter

how many members are being used.  When iSCSI sessions are created, each

session is connected to an eth port on a single member.  Data to a LUN

can be sent on any iSCSI session, and if the blocks being accessed are

stored on another member the I/O will be forwarded as required.  This

forwarding is invisible to the initiator.  The storage layout is also

dynamic, and the blocks stored on disk may be moved from member to

member as needed to balance the load.



This architecture simplifies the management and configuration of both

the storage group and initiators.  In a multipathing configuration, it

is possible to set up multiple iSCSI sessions to use multiple network

interfaces on both the host and target to take advantage of the

increased network bandwidth.  An initiator could use a simple round

robin algorithm to send I/O across all paths and let the storage array

members forward it as necessary, but there is a performance advantage to

sending data directly to the correct member.



A device-mapper table already lets you map different regions of a

device onto different targets.  However in this architecture the LUN is

spread with an address region size on the order of 10s of MBs, which

means the resulting table could have more than a million entries and

consume far too much memory.



Using this device-mapper switch target we can now build a two-layer

device hierarchy:



    Upper Tier – Determine which array member the I/O should be sent to.

    Lower Tier – Load balance amongst paths to a particular member.



The lower tier consists of a single dm multipath device for each member.

Each of these multipath devices contains the set of paths directly to

the array member in one priority group, and leverages existing path

selectors to load balance amongst these paths.  We also build a

non-preferred priority group containing paths to other array members for

failover reasons.



The upper tier consists of a single dm-switch device.  This device uses

a bitmap to look up the location of the I/O and choose the appropriate

lower tier device to route the I/O.  By using a bitmap we are able to

use 4 bits for each address range in a 16 member group (which is very

large for us).  This is a much denser representation than the dm table

b-tree can achieve.



Construction Parameters

=======================



    <num_paths> <region_size> <num_optional_args> [<optional_args>...]

    [<dev_path> <offset>]+



<num_paths>

    The number of paths across which to distribute the I/O.



<region_size>

    The number of 512-byte sectors in a region. Each region can be redirected

    to any of the available paths.



<num_optional_args>

    The number of optional arguments. Currently, no optional arguments

    are supported and so this must be zero.



<dev_path>

    The block device that represents a specific path to the device.



<offset>

    The offset of the start of data on the specific <dev_path> (in units

    of 512-byte sectors). This number is added to the sector number when

    forwarding the request to the specific path. Typically it is zero.



Messages

========



set_region_mappings <index>:<path_nr> [<index>]:<path_nr> [<index>]:<path_nr>...



Modify the region table by specifying which regions are redirected to

which paths.



<index>

    The region number (region size was specified in constructor parameters).

    If index is omitted, the next region (previous index + 1) is used.

    Expressed in hexadecimal (WITHOUT any prefix like 0x).



<path_nr>

    The path number in the range 0 ... (<num_paths> - 1).

    Expressed in hexadecimal (WITHOUT any prefix like 0x).



Status

======



No status line is reported.



Example

=======



Assume that you have volumes vg1/switch0 vg1/switch1 vg1/switch2 with

the same size.



Create a switch device with 64kB region size:

    dmsetup create switch --table "0 `blockdev --getsize /dev/vg1/switch0`

	switch 3 128 0 /dev/vg1/switch0 0 /dev/vg1/switch1 0 /dev/vg1/switch2 0"



Set mappings for the first 7 entries to point to devices switch0, switch1,

switch2, switch0, switch1, switch2, switch1:

    dmsetup message switch 0 set_region_mappings 0:0 :1 :2 :0 :1 :2 :1

MAINTAINERS

+2 −0
Original line number Diff line number Diff line
@@ -2574,6 +2574,7 @@ S: Maintained 


DEVICE-MAPPER  (LVM)

M:	Alasdair Kergon <agk@redhat.com>

M:	Mike Snitzer <snitzer@redhat.com>

M:	dm-devel@redhat.com

L:	dm-devel@redhat.com

W:	http://sources.redhat.com/dm
@@ -2585,6 +2586,7 @@ F: drivers/md/dm* 
F:	drivers/md/persistent-data/

F:	include/linux/device-mapper.h

F:	include/linux/dm-*.h

F:	include/uapi/linux/dm-*.h



DIOLAN U2C-12 I2C DRIVER

M:	Guenter Roeck <linux@roeck-us.net>

drivers/md/Kconfig

+14 −0
Original line number Diff line number Diff line
@@ -412,4 +412,18 @@ config DM_VERITY 


	  If unsure, say N.



config DM_SWITCH

	tristate "Switch target support (EXPERIMENTAL)"

	depends on BLK_DEV_DM

	---help---

	  This device-mapper target creates a device that supports an arbitrary

	  mapping of fixed-size regions of I/O across a fixed set of paths.

	  The path used for any specific region can be switched dynamically

	  by sending the target a message.



	  To compile this code as a module, choose M here: the module will

	  be called dm-switch.



	  If unsure, say N.



endif # MD

drivers/md/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -40,6 +40,7 @@ obj-$(CONFIG_DM_FLAKEY) += dm-flakey.o 
obj-$(CONFIG_DM_MULTIPATH)	+= dm-multipath.o dm-round-robin.o

obj-$(CONFIG_DM_MULTIPATH_QL)	+= dm-queue-length.o

obj-$(CONFIG_DM_MULTIPATH_ST)	+= dm-service-time.o

obj-$(CONFIG_DM_SWITCH)		+= dm-switch.o

obj-$(CONFIG_DM_SNAPSHOT)	+= dm-snapshot.o

obj-$(CONFIG_DM_PERSISTENT_DATA)	+= persistent-data/

obj-$(CONFIG_DM_MIRROR)		+= dm-mirror.o dm-log.o dm-region-hash.o

drivers/md/dm-bufio.c

+59 −16
Original line number Diff line number Diff line
@@ -145,6 +145,7 @@ struct dm_buffer { 
	unsigned long state;

	unsigned long last_accessed;

	struct dm_bufio_client *c;

	struct list_head write_list;

	struct bio bio;

	struct bio_vec bio_vec[DM_BUFIO_INLINE_VECS];

};
@@ -349,7 +350,7 @@ static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask, 
	if (gfp_mask & __GFP_NORETRY)

		noio_flag = memalloc_noio_save();



	ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);

	ptr = __vmalloc(c->block_size, gfp_mask | __GFP_HIGHMEM, PAGE_KERNEL);



	if (gfp_mask & __GFP_NORETRY)

		memalloc_noio_restore(noio_flag);
@@ -630,7 +631,8 @@ static int do_io_schedule(void *word) 
 * - Submit our write and don't wait on it. We set B_WRITING indicating

 *   that there is a write in progress.

 */

static void __write_dirty_buffer(struct dm_buffer *b)

static void __write_dirty_buffer(struct dm_buffer *b,

				 struct list_head *write_list)

{

	if (!test_bit(B_DIRTY, &b->state))

		return;
@@ -639,7 +641,24 @@ static void __write_dirty_buffer(struct dm_buffer *b) 
	wait_on_bit_lock(&b->state, B_WRITING,

			 do_io_schedule, TASK_UNINTERRUPTIBLE);



	if (!write_list)

		submit_io(b, WRITE, b->block, write_endio);

	else

		list_add_tail(&b->write_list, write_list);

}



static void __flush_write_list(struct list_head *write_list)

{

	struct blk_plug plug;

	blk_start_plug(&plug);

	while (!list_empty(write_list)) {

		struct dm_buffer *b =

			list_entry(write_list->next, struct dm_buffer, write_list);

		list_del(&b->write_list);

		submit_io(b, WRITE, b->block, write_endio);

		dm_bufio_cond_resched();

	}

	blk_finish_plug(&plug);

}



/*
@@ -655,7 +674,7 @@ static void __make_buffer_clean(struct dm_buffer *b) 
		return;



	wait_on_bit(&b->state, B_READING, do_io_schedule, TASK_UNINTERRUPTIBLE);

	__write_dirty_buffer(b);

	__write_dirty_buffer(b, NULL);

	wait_on_bit(&b->state, B_WRITING, do_io_schedule, TASK_UNINTERRUPTIBLE);

}
@@ -802,7 +821,8 @@ static void __free_buffer_wake(struct dm_buffer *b) 
	wake_up(&c->free_buffer_wait);

}



static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait)

static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait,

					struct list_head *write_list)

{

	struct dm_buffer *b, *tmp;
@@ -818,7 +838,7 @@ static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait) 
		if (no_wait && test_bit(B_WRITING, &b->state))

			return;



		__write_dirty_buffer(b);

		__write_dirty_buffer(b, write_list);

		dm_bufio_cond_resched();

	}

}
@@ -853,7 +873,8 @@ static void __get_memory_limit(struct dm_bufio_client *c, 
 * If we are over threshold_buffers, start freeing buffers.

 * If we're over "limit_buffers", block until we get under the limit.

 */

static void __check_watermark(struct dm_bufio_client *c)

static void __check_watermark(struct dm_bufio_client *c,

			      struct list_head *write_list)

{

	unsigned long threshold_buffers, limit_buffers;
@@ -872,7 +893,7 @@ static void __check_watermark(struct dm_bufio_client *c) 
	}



	if (c->n_buffers[LIST_DIRTY] > threshold_buffers)

		__write_dirty_buffers_async(c, 1);

		__write_dirty_buffers_async(c, 1, write_list);

}



/*
@@ -897,7 +918,8 @@ static struct dm_buffer *__find(struct dm_bufio_client *c, sector_t block) 
 *--------------------------------------------------------------*/



static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,

				     enum new_flag nf, int *need_submit)

				     enum new_flag nf, int *need_submit,

				     struct list_head *write_list)

{

	struct dm_buffer *b, *new_b = NULL;
@@ -924,7 +946,7 @@ static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block, 
		goto found_buffer;

	}



	__check_watermark(c);

	__check_watermark(c, write_list);



	b = new_b;

	b->hold_count = 1;
@@ -992,10 +1014,14 @@ static void *new_read(struct dm_bufio_client *c, sector_t block, 
	int need_submit;

	struct dm_buffer *b;



	LIST_HEAD(write_list);



	dm_bufio_lock(c);

	b = __bufio_new(c, block, nf, &need_submit);

	b = __bufio_new(c, block, nf, &need_submit, &write_list);

	dm_bufio_unlock(c);



	__flush_write_list(&write_list);



	if (!b)

		return b;
@@ -1047,6 +1073,8 @@ void dm_bufio_prefetch(struct dm_bufio_client *c, 
{

	struct blk_plug plug;



	LIST_HEAD(write_list);



	BUG_ON(dm_bufio_in_request());



	blk_start_plug(&plug);
@@ -1055,7 +1083,15 @@ void dm_bufio_prefetch(struct dm_bufio_client *c, 
	for (; n_blocks--; block++) {

		int need_submit;

		struct dm_buffer *b;

		b = __bufio_new(c, block, NF_PREFETCH, &need_submit);

		b = __bufio_new(c, block, NF_PREFETCH, &need_submit,

				&write_list);

		if (unlikely(!list_empty(&write_list))) {

			dm_bufio_unlock(c);

			blk_finish_plug(&plug);

			__flush_write_list(&write_list);

			blk_start_plug(&plug);

			dm_bufio_lock(c);

		}

		if (unlikely(b != NULL)) {

			dm_bufio_unlock(c);
@@ -1069,7 +1105,6 @@ void dm_bufio_prefetch(struct dm_bufio_client *c, 
				goto flush_plug;

			dm_bufio_lock(c);

		}



	}



	dm_bufio_unlock(c);
@@ -1126,11 +1161,14 @@ EXPORT_SYMBOL_GPL(dm_bufio_mark_buffer_dirty); 


void dm_bufio_write_dirty_buffers_async(struct dm_bufio_client *c)

{

	LIST_HEAD(write_list);



	BUG_ON(dm_bufio_in_request());



	dm_bufio_lock(c);

	__write_dirty_buffers_async(c, 0);

	__write_dirty_buffers_async(c, 0, &write_list);

	dm_bufio_unlock(c);

	__flush_write_list(&write_list);

}

EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers_async);
@@ -1147,8 +1185,13 @@ int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c) 
	unsigned long buffers_processed = 0;

	struct dm_buffer *b, *tmp;



	LIST_HEAD(write_list);



	dm_bufio_lock(c);

	__write_dirty_buffers_async(c, 0, &write_list);

	dm_bufio_unlock(c);

	__flush_write_list(&write_list);

	dm_bufio_lock(c);

	__write_dirty_buffers_async(c, 0);



again:

	list_for_each_entry_safe_reverse(b, tmp, &c->lru[LIST_DIRTY], lru_list) {
@@ -1274,7 +1317,7 @@ retry: 
	BUG_ON(!b->hold_count);

	BUG_ON(test_bit(B_READING, &b->state));



	__write_dirty_buffer(b);

	__write_dirty_buffer(b, NULL);

	if (b->hold_count == 1) {

		wait_on_bit(&b->state, B_WRITING,

			    do_io_schedule, TASK_UNINTERRUPTIBLE);

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