When we break sharing on btree nodes we typically need to increment
the reference counts to every value held in the node. This can
cause a lot of repeated calls to the space maps. Fix this by changing
the interface to the space map inc/dec methods to take ranges of
adjacent blocks to be operated on.
For installations that are using a lot of snapshots this will reduce
cpu overhead of fundamental operations such as provisioning a new block,
or deleting a snapshot, by as much as 10 times.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit improves the residency of btrees built in the metadata for
dm-thin and dm-cache.
When inserting a new entry into a full btree node the current code
splits the node into two. This can result in very many half full nodes,
particularly if the insertions are occurring in an ascending order (as
happens in dm-thin with large writes).
With this commit, when we insert into a full node we first try and move
some entries to a neighbouring node that has space, failing that it
tries to split two neighbouring nodes into three.
Results are given below. 'Residency' is how full nodes are on average
as a percentage. Average instruction counts for the operations
are given to show the extra processing has little overhead.
+--------------------------+--------------------------+
| Before | After |
+------------+-----------+-----------+--------------+-----------+--------------+
| Test | Phase | Residency | Instructions | Residency | Instructions |
+------------+-----------+-----------+--------------+-----------+--------------+
| Ascending | insert | 50 | 1876 | 96 | 1930 |
| | overwrite | 50 | 1789 | 96 | 1746 |
| | lookup | 50 | 778 | 96 | 778 |
| Descending | insert | 50 | 3024 | 96 | 3181 |
| | overwrite | 50 | 1789 | 96 | 1746 |
| | lookup | 50 | 778 | 96 | 778 |
| Random | insert | 68 | 3800 | 84 | 3736 |
| | overwrite | 68 | 4254 | 84 | 3911 |
| | lookup | 68 | 779 | 84 | 779 |
| Runs | insert | 63 | 2546 | 82 | 2815 |
| | overwrite | 63 | 2013 | 82 | 1986 |
| | lookup | 63 | 778 | 82 | 779 |
+------------+-----------+-----------+--------------+-----------+--------------+
Ascending - keys are inserted in ascending order.
Descending - keys are inserted in descending order.
Random - keys are inserted in random order.
Runs - keys are split into ascending runs of ~20 length. Then
the runs are shuffled.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com> # contains_key() fix
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
dm_bm_unlock and dm_tm_unlock return an integer value but the returned
value is always 0. The calling code sometimes checks the return value
and sometimes doesn't.
Eliminate these unnecessary return values and also the checks for them.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Introduce the dm_tm_issue_prefetches interface. If you're using a
non-blocking clone the tm will build up a list of requested blocks that
weren't in core. dm_tm_issue_prefetches will request those blocks to be
prefetched.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
The persistent-data library used by dm-thin, dm-cache, etc is
transactional. If anything goes wrong, such as an io error when writing
new metadata or a power failure, then we roll back to the last
transaction.
Atomicity when committing a transaction is achieved by:
a) Never overwriting data from the previous transaction.
b) Writing the superblock last, after all other metadata has hit the
disk.
This commit and the following commit ("dm: take care to copy the space
map roots before locking the superblock") fix a bug associated with (b).
When committing it was possible for the superblock to still be written
in spite of an io error occurring during the preceeding metadata flush.
With these commits we're careful not to take the write lock out on the
superblock until after the metadata flush has completed.
Change the transaction manager's semantics for dm_tm_commit() to assume
all data has been flushed _before_ the single superblock that is passed
in.
As a prerequisite, split the block manager's block unlocking and
flushing by simplifying dm_bm_flush_and_unlock() to dm_bm_flush(). Now
the unlocking must be done separately.
This issue was discovered by forcing io errors at the crucial time
using dm-flakey.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Tidy the transaction manager creation functions.
They no longer lock the superblock. Superblock locking is pulled out to
the caller.
Also export dm_bm_write_lock_zero.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
The persistent-data library offers a re-usable framework for the storage
and management of on-disk metadata in device-mapper targets.
It's used by the thin-provisioning target in the next patch and in an
upcoming hierarchical storage target.
For further information, please read
Documentation/device-mapper/persistent-data.txt
Signed-off-by: Joe Thornber <thornber@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
