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Mikulas Patocka b1d5552838 dm snapshot: implement merge 
Implement merge method for the snapshot origin to improve read
performance.

Without merge method, dm asks the upper layers to submit smallest possible
bios --- one page. Submitting such small bios impacts performance negatively
when reading or writing the origin device.

Without this patch, CPU consumption when reading the origin on lvm on md-raid0
was 6 to 12%, with this patch, it drops to 1 to 4%.

Note: in my testing, it actually degraded performance in some settings, I
traced it to Maxtor disks having problems with > 512-sector requests.
Reducing the number of sectors to /sys/block/sd*/queue/max_sectors_kb to
256 fixed the read performance. I think we don't have to care about weird
disks that actually degrade performance because of large requests being
sent to them.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
 		2010-08-12 04:14:02 +01:00
..
.gitignore
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Kconfig Merge branch 'async' of macbook:git/btrfs-unstable 2010-08-09 10:36:44 +01:00
Makefile Merge branch 'async' of macbook:git/btrfs-unstable 2010-08-09 10:36:44 +01:00
bitmap.c md/bitmap: separate out loading a bitmap from initialising the structures. 2010-07-26 13:21:34 +10:00
bitmap.h md/bitmap: separate out loading a bitmap from initialising the structures. 2010-07-26 13:21:34 +10:00
dm-bio-record.h
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dm-crypt.c dm crypt: use kstrdup 2010-08-12 04:13:58 +01:00
dm-delay.c dm table: remove unused dm_get_device range parameters 2010-03-06 02:32:27 +00:00
dm-exception-store.c dm snapshot: test chunk size against both origin and snapshot 2010-08-12 04:13:51 +01:00
dm-exception-store.h dm snapshot: test chunk size against both origin and snapshot 2010-08-12 04:13:51 +01:00
dm-io.c block: unify flags for struct bio and struct request 2010-08-07 18:20:39 +02:00
dm-ioctl.c dm: do not initialise full request queue when bio based 2010-08-12 04:14:02 +01:00
dm-kcopyd.c block: unify flags for struct bio and struct request 2010-08-07 18:20:39 +02:00
dm-linear.c dm table: remove unused dm_get_device range parameters 2010-03-06 02:32:27 +00:00
dm-log-userspace-base.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
dm-log-userspace-transfer.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
dm-log-userspace-transfer.h dm log: userspace add luid to distinguish between concurrent log instances 2009-09-04 20:40:34 +01:00
dm-log.c dm table: remove unused dm_get_device range parameters 2010-03-06 02:32:27 +00:00
dm-mpath.c dm mpath: fix NULL pointer dereference when path parameters missing 2010-08-12 04:13:49 +01:00
dm-mpath.h
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dm-path-selector.c
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dm-path-selector.h
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dm-queue-length.c
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dm-raid1.c block: unify flags for struct bio and struct request 2010-08-07 18:20:39 +02:00
dm-region-hash.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
dm-round-robin.c
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dm-service-time.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
dm-snap-persistent.c dm snapshot: persistent use define for disk header chunk size 2010-08-12 04:13:59 +01:00
dm-snap-transient.c dm snapshot: move cow ref from exception store to snap core 2009-12-10 23:52:12 +00:00
dm-snap.c dm snapshot: implement merge 2010-08-12 04:14:02 +01:00
dm-stripe.c block: unify flags for struct bio and struct request 2010-08-07 18:20:39 +02:00
dm-sysfs.c Driver core: Constify struct sysfs_ops in struct kobj_type 2010-03-07 17:04:49 -08:00
dm-table.c dm table: remove unused dm_get_device range parameters 2010-03-06 02:32:27 +00:00
dm-target.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
dm-uevent.c dm table: remove dm_get from dm_table_get_md 2010-03-06 02:29:52 +00:00
dm-uevent.h
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dm-zero.c
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dm.c dm: do not initialise full request queue when bio based 2010-08-12 04:14:02 +01:00
dm.h dm: do not initialise full request queue when bio based 2010-08-12 04:14:02 +01:00
faulty.c Merge commit '3ff195b011d7decf501a4d55aeed312731094796' into for-linus 2010-05-22 08:31:36 +10:00
linear.c block: unify flags for struct bio and struct request 2010-08-07 18:20:39 +02:00
linear.h
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md.c Merge branch 'for-linus' of git://neil.brown.name/md 2010-08-10 15:38:19 -07:00
md.h Merge branch 'for-linus' of git://neil.brown.name/md 2010-08-10 15:38:19 -07:00
multipath.c block: unify flags for struct bio and struct request 2010-08-07 18:20:39 +02:00
multipath.h
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raid0.c block: unify flags for struct bio and struct request 2010-08-07 18:20:39 +02:00
raid0.h md: fix handling of array level takeover that re-arranges devices. 2010-06-24 13:33:24 +10:00
raid1.c block: unify flags for struct bio and struct request 2010-08-07 18:20:39 +02:00
raid1.h md/raid1: add takeover support for raid5->raid1 2009-12-14 12:51:41 +11:00
raid5.c Merge branch 'for-linus' of git://neil.brown.name/md 2010-08-10 15:38:19 -07:00
raid5.h md/raid5: export raid5 unplugging interface. 2010-07-26 12:53:10 +10:00
raid10.c Merge branch 'for-linus' of git://neil.brown.name/md 2010-08-10 15:38:19 -07:00
raid10.h md: fix handling of array level takeover that re-arranges devices. 2010-06-24 13:33:24 +10:00