linux-stable.git/drivers/md/dm-snap.c, branch linux-2.6.36.y

dm: rename map_info flush_request to target_request_nr

2010-08-12T03:14:04+00:00

'target_request_nr' is a more generic name that reflects the fact that
it will be used for both flush and discard support.

Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm snapshot: implement merge

2010-08-12T03:14:02+00:00

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 
Signed-off-by: Alasdair G Kergon

dm snapshot: test chunk size against both origin and snapshot

2010-08-12T03:13:51+00:00

Validate chunk size against both origin and snapshot sector size

Don't allow chunk size smaller than either origin or snapshot logical
sector size. Reading or writing data not aligned to sector size is not
allowed and causes immediate errors.

This requires us to open the origin before initialising the
exception store and to export dm_snap_origin.

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka 
Reviewed-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm snapshot: iterate origin and cow devices

2010-08-12T03:13:50+00:00

Iterate both origin and snapshot devices

iterate_devices method should call the callback for all the devices where
the bio may be remapped. Thus, snapshot_iterate_devices should call the callback
for both snapshot and origin underlying devices because it remaps some bios
to the snapshot and some to the origin.

snapshot_iterate_devices called the callback only for the origin device.
This led to badly calculated device limits if snapshot and origin were placed
on different types of disks.

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka 
Reviewed-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm: eliminate some holes data structures

2010-03-06T02:32:33+00:00

Eliminate a 4-byte hole in 'struct dm_io_memory' by moving 'offset' above the
'ptr' to which it applies (size reduced from 24 to 16 bytes).  And by
association, 1-4 byte hole is eliminated in 'struct dm_io_request' (size
reduced from 56 to 48 bytes).

Eliminate all 6 4-byte holes and 1 cache-line in 'struct dm_snapshot' (size
reduced from 392 to 368 bytes).

Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm table: remove unused dm_get_device range parameters

2010-03-06T02:32:27+00:00

Remove unused parameters(start and len) of dm_get_device()
and fix the callers.

Signed-off-by: Nikanth Karthikesan 
Signed-off-by: Alasdair G Kergon

dm snapshot: use merge origin if snapshot invalid

2009-12-10T23:52:36+00:00

If the snapshot we are merging became invalid (e.g. it ran out of
space) redirect all I/O directly to the origin device.

Signed-off-by: Mikulas Patocka 
Reviewed-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm snapshot: report merge failure in status

2009-12-10T23:52:35+00:00

Set 'merge_failed' flag if a snapshot fails to merge.  Update
snapshot_status() to report "Merge failed" if 'merge_failed' is set.

Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm snapshot: merge consecutive chunks together

2009-12-10T23:52:34+00:00

s->store->type->prepare_merge returns the number of chunks that can be
copied linearly working backwards from the returned chunk number.

For example, if it returns 3 chunks with old_chunk == 10 and new_chunk
== 20, then chunk 20 can be copied to 10, chunk 19 to 9 and 18 to 8.

Until now kcopyd only copied one chunk at a time.  This patch now copies
the full set at once.

Consequently, snapshot_merge_process() needs to delay the merging of all
chunks if any have writes in progress, not just the first chunk in the
region that is to be merged.

snapshot-merge's performance is now comparable to the original
snapshot-origin target.

Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm snapshot: trigger exceptions in remaining snapshots during merge

2009-12-10T23:52:34+00:00

When there is one merging snapshot and other non-merging snapshots,
snapshot_merge_process() must make exceptions in the non-merging
snapshots.

Use a sequence count to resolve the race between I/O to chunks that are
about to be merged.  The count increases each time an exception
reallocation finishes.  Use wait_event() to wait until the count
changes.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon