linux/drivers/md
Kiyoshi Ueda f40c67f0f7 dm mpath: change to be request based
This patch converts dm-multipath target to request-based from bio-based.

Basically, the patch just converts the I/O unit from struct bio
to struct request.
In the course of the conversion, it also changes the I/O queueing
mechanism.  The change in the I/O queueing is described in details
as follows.

I/O queueing mechanism change
-----------------------------
In I/O submission, map_io(), there is no mechanism change from
bio-based, since the clone request is ready for retry as it is.
However, in I/O complition, do_end_io(), there is a mechanism change
from bio-based, since the clone request is not ready for retry.

In do_end_io() of bio-based, the clone bio has all needed memory
for resubmission.  So the target driver can queue it and resubmit
it later without memory allocations.
The mechanism has almost no overhead.

On the other hand, in do_end_io() of request-based, the clone request
doesn't have clone bios, so the target driver can't resubmit it
as it is.  To resubmit the clone request, memory allocation for
clone bios is needed, and it takes some overheads.
To avoid the overheads just for queueing, the target driver doesn't
queue the clone request inside itself.
Instead, the target driver asks dm core for queueing and remapping
the original request of the clone request, since the overhead for
queueing is just a freeing memory for the clone request.

As a result, the target driver doesn't need to record/restore
the information of the original request for resubmitting
the clone request.  So dm_bio_details in dm_mpath_io is removed.

multipath_busy()
---------------------
The target driver returns "busy", only when the following case:
  o The target driver will map I/Os, if map() function is called
  and
  o The mapped I/Os will wait on underlying device's queue due to
    their congestions, if map() function is called now.

In other cases, the target driver doesn't return "busy".
Otherwise, dm core will keep the I/Os and the target driver can't
do what it wants.
(e.g. the target driver can't map I/Os now, so wants to kill I/Os.)

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Acked-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2009-06-22 10:12:37 +01:00
..
raid6test
.gitignore
bitmap.c Merge branch 'for-2.6.31' of git://git.kernel.dk/linux-2.6-block 2009-06-11 11:10:35 -07:00
bitmap.h
dm-bio-record.h
dm-crypt.c dm target:s introduce iterate devices fn 2009-06-22 10:12:33 +01:00
dm-delay.c dm target:s introduce iterate devices fn 2009-06-22 10:12:33 +01:00
dm-exception-store.c dm exception store: fix exstore lookup to be case insensitive 2009-06-22 10:12:15 +01:00
dm-exception-store.h dm: use i_size_read 2009-06-22 10:12:14 +01:00
dm-io.c dm io: retry after barrier error 2009-06-22 10:12:26 +01:00
dm-ioctl.c dm: enable request based option 2009-06-22 10:12:36 +01:00
dm-kcopyd.c dm kcopyd: fix callback race 2009-04-09 00:27:17 +01:00
dm-linear.c dm target:s introduce iterate devices fn 2009-06-22 10:12:33 +01:00
dm-log-userspace-base.c dm raid1: add userspace log 2009-06-22 10:12:35 +01:00
dm-log-userspace-transfer.c dm raid1: add userspace log 2009-06-22 10:12:35 +01:00
dm-log-userspace-transfer.h dm raid1: add userspace log 2009-06-22 10:12:35 +01:00
dm-log.c dm log: fix create_log_context to use logical_block_size of log device 2009-06-22 10:12:33 +01:00
dm-mpath.c dm mpath: change to be request based 2009-06-22 10:12:37 +01:00
dm-mpath.h
dm-path-selector.c
dm-path-selector.h dm mpath: add start_io and nr_bytes to path selectors 2009-06-22 10:12:27 +01:00
dm-queue-length.c dm mpath: add queue length load balancer 2009-06-22 10:12:27 +01:00
dm-raid1.c dm target:s introduce iterate devices fn 2009-06-22 10:12:33 +01:00
dm-region-hash.c dm raid1: keep retrying alloc if mempool_alloc failed 2009-06-22 10:12:13 +01:00
dm-round-robin.c dm mpath: add start_io and nr_bytes to path selectors 2009-06-22 10:12:27 +01:00
dm-service-time.c dm mpath: add service time load balancer 2009-06-22 10:12:28 +01:00
dm-snap-persistent.c dm snapshot: use barrier when writing exception store 2009-06-22 10:12:26 +01:00
dm-snap-transient.c
dm-snap.c dm snapshot: support barriers 2009-06-22 10:12:25 +01:00
dm-stripe.c dm target:s introduce iterate devices fn 2009-06-22 10:12:33 +01:00
dm-sysfs.c dm: sysfs add suspended attribute 2009-06-22 10:12:29 +01:00
dm-table.c dm: do not set QUEUE_ORDERED_DRAIN if request based 2009-06-22 10:12:36 +01:00
dm-target.c
dm-uevent.c
dm-uevent.h
dm-zero.c
dm.c dm: disable interrupt when taking map_lock 2009-06-22 10:12:37 +01:00
dm.h dm: do not set QUEUE_ORDERED_DRAIN if request based 2009-06-22 10:12:36 +01:00
faulty.c md: Move check for bitmap presence to personality code. 2009-06-18 08:49:23 +10:00
Kconfig dm raid1: add userspace log 2009-06-22 10:12:35 +01:00
linear.c md/linear: use call_rcu to free obsolete 'conf' structures. 2009-06-18 08:49:42 +10:00
linear.h md/linear: use call_rcu to free obsolete 'conf' structures. 2009-06-18 08:49:42 +10:00
Makefile dm raid1: add userspace log 2009-06-22 10:12:35 +01:00
md.c md: Move check for bitmap presence to personality code. 2009-06-18 08:49:23 +10:00
md.h md: Move check for bitmap presence to personality code. 2009-06-18 08:49:23 +10:00
mktables.c
multipath.c md: Move check for bitmap presence to personality code. 2009-06-18 08:49:23 +10:00
multipath.h md: remove mddev_to_conf "helper" macro 2009-06-16 16:54:21 +10:00
raid0.c md: Move check for bitmap presence to personality code. 2009-06-18 08:49:23 +10:00
raid0.h md: remove mddev_to_conf "helper" macro 2009-06-16 16:54:21 +10:00
raid1.c md: Push down reconstruction log message to personality code. 2009-06-18 08:48:06 +10:00
raid1.h md: remove mddev_to_conf "helper" macro 2009-06-16 16:54:21 +10:00
raid5.c md/raid5: correctly update sync_completed when we reach max_resync 2009-06-18 09:14:12 +10:00
raid5.h md: convert conf->chunk_size and conf->prev_chunk to sectors. 2009-06-18 08:45:55 +10:00
raid6algos.c
raid6altivec.uc
raid6int.uc
raid6mmx.c
raid6recov.c
raid6sse1.c
raid6sse2.c
raid6x86.h
raid10.c md: Push down reconstruction log message to personality code. 2009-06-18 08:48:06 +10:00
raid10.h md: remove mddev_to_conf "helper" macro 2009-06-16 16:54:21 +10:00
unroll.pl