linux.git/drivers/md/dm-cache-target.c, branch v3.19

dm cache: fix problematic dual use of a single migration count variable

2015-01-23T16:06:08+00:00

Introduce a new variable to count the number of allocated migration
structures.  The existing variable cache->nr_migrations became
overloaded.  It was used to:

 i) track of the number of migrations in flight for the purposes of
    quiescing during suspend.

 ii) to estimate the amount of background IO occuring.

Recent discard changes meant that REQ_DISCARD bios are processed with
a migration.  Discards are not background IO so nr_migrations was not
incremented.  However this could cause quiescing to complete early.

(i) is now handled with a new variable cache->nr_allocated_migrations.
cache->nr_migrations has been renamed cache->nr_io_migrations.
cleanup_migration() is now called free_io_migration(), since it
decrements that variable.

Also, remove the unused cache->next_migration variable that got replaced
with with prealloc_structs a while ago.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Cc: stable@vger.kernel.org

dm cache: fix spurious cell_defer when dealing with partial block at end of device

2014-12-01T16:30:13+00:00

We never bother caching a partial block that is at the back end of the
origin device.  No cell ever gets locked, but the calling code was
assuming it was and trying to release it.

Now the code only releases if the cell has been set to a non NULL
value.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Cc: stable@vger.kernel.org

dm cache: dirty flag was mistakenly being cleared when promoting via overwrite

2014-12-01T16:30:12+00:00

If the incoming bio is a WRITE and completely covers a block then we
don't bother to do any copying for a promotion operation.  Once this is
done the cache block and origin block will be different, so we need to
set it to 'dirty'.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Cc: stable@vger.kernel.org

dm cache: only use overwrite optimisation for promotion when in writeback mode

2014-12-01T16:30:12+00:00

Overwrite causes the cache block and origin blocks to diverge, which
is only allowed in writeback mode.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Cc: stable@vger.kernel.org

dm cache: discard block size must be a multiple of cache block size

2014-12-01T16:30:11+00:00

Otherwise the cache blocks may span two discard blocks, which we don't
handle when doing the discard lookup.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer

dm cache: fix a harmless race when working out if a block is discarded

2014-12-01T16:30:11+00:00

It is more correct to hold the cell before checking the discard state.
These flags are only used as hints to the policy so this change will
have negligable effect.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer

dm cache: when reloading a discard bitset allow for a different discard block size

2014-12-01T16:30:10+00:00

The discard block size can change if the origin changes size or if an
old DM cache is upgraded from using a discard block size that was equal
to cache block size.

To fix this an extent of discarded blocks is established for the purpose
of translating the old discard block size to the new in-core discard
block size and set bits.  The old (potentially huge) discard bitset is
left ondisk until it is re-written using the new in-core information on
the next successful DM cache shutdown.

Fixes: 7ae34e777896 ("dm cache: improve discard support")
Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer

dm cache: fix some issues with the new discard range support

2014-12-01T16:30:09+00:00

Commit 7ae34e777 ("dm cache: improve discard support") needed to also:
- discontinue having DM core split the discard bios on cache block
  boundaries
- calculate the cache's discard_nr_blocks relative to the determined
  discard_block_size rather than using oblock_to_dblock()

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer

dm cache: emit a warning message if there are a lot of cache blocks

2014-11-13T01:14:59+00:00

Loading and saving millions of block mappings takes time.  We may as
well explain what's going on, and encourage people to use a larger
cache block size.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer

dm cache: improve discard support

2014-11-10T20:25:30+00:00

Safely allow the discard blocksize to be larger than the cache blocksize
by using the bio prison's range locking support.  This also improves
discard performance considerly because larger discards are issued to the
dm-cache device.  The discard blocksize was always intended to be
greater than the cache blocksize.  But until now it wasn't implemented
safely.

Also, by safely restoring the ability to have discard blocksize larger
than cache blocksize we're able to significantly reduce the memory used
for the cache's discard bitset.  Before, with a small discard blocksize,
the discard bitset could get quite large because its size is a function
of the discard blocksize and the origin device's size.  For example,
previously, using a 32KB cache blocksize with a 40TB origin resulted in
1280MB of incore memory use for the discard bitset!  Now, the discard
blocksize is scaled up accordingly to ensure the discard bitset is
capped at 2**14 bits, or 16KB.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer