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When using caches with BIG pool size (>TB) there is required
to use relatively huge chunk size. Once the chunksize has
got over 1MiB - kernel cache target stopped writing such chunks
back on this if the migration_threshold remained on default 1MiB
(2048 sectors) size.
This patch ensure, DM layer will not let pass table line which
has not big enough migration threshold that can let pass
at least 8 chunks (independently of lvm2 metadata).
Drop very old original format of VDO target and focus on V2 version.
So some variables were renamed or replaced.
There is no compatibility preserved (with assumption so far this is
experimental feature and there is no real user).
Note - version currently VDO calls this version 6.2.
This could be seen as continuation of
6cee8f1b06.
Some test maching with old udev system shows problem,
where udev 'jumps on' leg device after mirror target
releases its legs - since udev does not (in this old case) skips
such device from scanning - it opens device - and this prevent
leg device to be deactivated - effectively such device stays
'leaked' in DM table invisibly to lvm2 command.
So to 'combat' this issue - if the device has '_mimage' in its name,
the retry of deactivation is automatically assumed.
NOTE: wider impact is unexpected - as it's touching only old mirror
target which is nowadays replaced with 'raid'.
In case there will be some problem identified - probably both patches
should be reverted.
With older systems and udevs we don't have control over scanning of lvm2
internal devices - so far we set retry-removal only for top-level LVs,
but in occasional cases udev can be 'fast enough' to open device for
scanning and prevent removal of such device from DM table.
So to combat this case - try to pass 'retry' flag also for removal of
internal device so see how many races can go away with this simple
patch.
Note: patch is applied only to internal version of libdm so the external
API remains working in the old way for now.
If a single, standard LV is specified as the cache, use
it directly instead of converting it into a cache-pool
object with two separate LVs (for data and metadata).
With a single LV as the cache, lvm will use blocks at the
beginning for metadata, and the rest for data. Separate
dm linear devices are set up to point at the metadata and
data areas of the LV. These dm devs are given to the
dm-cache target to use.
The single LV cache cannot be resized without recreating it.
If the --poolmetadata option is used to specify an LV for
metadata, then a cache pool will be created (with separate
LVs for data and metadata.)
Usage:
$ lvcreate -n main -L 128M vg /dev/loop0
$ lvcreate -n fast -L 64M vg /dev/loop1
$ lvs -a vg
LV VG Attr LSize Type Devices
main vg -wi-a----- 128.00m linear /dev/loop0(0)
fast vg -wi-a----- 64.00m linear /dev/loop1(0)
$ lvconvert --type cache --cachepool fast vg/main
$ lvs -a vg
LV VG Attr LSize Origin Pool Type Devices
[fast] vg Cwi---C--- 64.00m linear /dev/loop1(0)
main vg Cwi---C--- 128.00m [main_corig] [fast] cache main_corig(0)
[main_corig] vg owi---C--- 128.00m linear /dev/loop0(0)
$ lvchange -ay vg/main
$ dmsetup ls
vg-fast_cdata (253:4)
vg-fast_cmeta (253:5)
vg-main_corig (253:6)
vg-main (253:24)
vg-fast (253:3)
$ dmsetup table
vg-fast_cdata: 0 98304 linear 253:3 32768
vg-fast_cmeta: 0 32768 linear 253:3 0
vg-main_corig: 0 262144 linear 7:0 2048
vg-main: 0 262144 cache 253:5 253:4 253:6 128 2 metadata2 writethrough mq 0
vg-fast: 0 131072 linear 7:1 2048
$ lvchange -an vg/min
$ lvconvert --splitcache vg/main
$ lvs -a vg
LV VG Attr LSize Type Devices
fast vg -wi------- 64.00m linear /dev/loop1(0)
main vg -wi------- 128.00m linear /dev/loop0(0)
When node loading fails, there is not much the caller can do,
since there is 'unknown' set of devices preloaded.
Only suspend during preload knows future precommitted 'metadata',
so it's non-trivial to drop 'preloaded' entries with any later call.
However dm tree tracks newly loaded entries - so in this case it
may simplify the recovery path by dropping preloaded entries so
they are not leaked in the DM table.
For better code reuse split _node_send_messages into commont
messaging part and separate _thin_pool_node_send_messages.
Patch makes it possible to better reuse common code for messaging
other targets.
The device-mapper directory now holds a copy of libdm source. At
the moment this code is identical to libdm. Over time code will
migrate out to appropriate places (see doc/refactoring.txt).
The libdm directory still exists, and contains the source for the
libdevmapper shared library, which we will continue to ship (though
not neccessarily update).
All code using libdm should now use the version in device-mapper.
