Commit Graph

16 Commits

Author SHA1 Message Date
Wu Fengguang d4a789474a Btrfs: fix typos in comments
Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-04-02 16:46:06 -04:00
Chris Mason b9473439d3 Btrfs: leave btree locks spinning more often
btrfs_mark_buffer dirty would set dirty bits in the extent_io tree
for the buffers it was dirtying.  This may require a kmalloc and it
was not atomic.  So, anyone who called btrfs_mark_buffer_dirty had to
set any btree locks they were holding to blocking first.

This commit changes dirty tracking for extent buffers to just use a flag
in the extent buffer.  Now that we have one and only one extent buffer
per page, this can be safely done without losing dirty bits along the way.

This also introduces a path->leave_spinning flag that callers of
btrfs_search_slot can use to indicate they will properly deal with a
path returned where all the locks are spinning instead of blocking.

Many of the btree search callers now expect spinning paths,
resulting in better btree concurrency overall.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-03-24 16:14:28 -04:00
Chris Mason 66d7e85ea7 Btrfs: Check for a blocking lock before taking the spin
This reduces contention on the extent buffer spin locks by testing for a
blocking lock before trying to take the spinlock.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-03-24 16:14:27 -04:00
Chris Mason b9447ef80b Btrfs: fix spinlock assertions on UP systems
btrfs_tree_locked was being used to make sure a given extent_buffer was
properly locked in a few places.  But, it wasn't correct for UP compiled
kernels.

This switches it to using assert_spin_locked instead, and renames it to
btrfs_assert_tree_locked to better reflect how it was really being used.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-03-09 11:45:38 -04:00
Chris Mason 4008c04a07 Btrfs: make a lockdep class for the extent buffer locks
Btrfs is currently using spin_lock_nested with a nested value based
on the tree depth of the block.  But, this doesn't quite work because
the max tree depth is bigger than what spin_lock_nested can deal with,
and because locks are sometimes taken before the level field is filled in.

The solution here is to use lockdep_set_class_and_name instead, and to
set the class before unlocking the pages when the block is read from the
disk and just after init of a freshly allocated tree block.

btrfs_clear_path_blocking is also changed to take the locks in the proper
order, and it also makes sure all the locks currently held are properly
set to blocking before it tries to retake the spinlocks.  Otherwise, lockdep
gets upset about bad lock orderin.

The lockdep magic cam from Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-02-12 14:09:45 -05:00
Chris Mason 284b066af4 Btrfs: don't use spin_is_contended
Btrfs was using spin_is_contended to see if it should drop locks before
doing extent allocations during btrfs_search_slot.  The idea was to avoid
expensive searches in the tree unless the lock was actually contended.

But, spin_is_contended is specific to the ticket spinlocks on x86, so this
is causing compile errors everywhere else.

In practice, the contention could easily appear some time after we started
doing the extent allocation, and it makes more sense to always drop the lock
instead.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-02-09 16:22:03 -05:00
Chris Mason b4ce94de9b Btrfs: Change btree locking to use explicit blocking points
Most of the btrfs metadata operations can be protected by a spinlock,
but some operations still need to schedule.

So far, btrfs has been using a mutex along with a trylock loop,
most of the time it is able to avoid going for the full mutex, so
the trylock loop is a big performance gain.

This commit is step one for getting rid of the blocking locks entirely.
btrfs_tree_lock takes a spinlock, and the code explicitly switches
to a blocking lock when it starts an operation that can schedule.

We'll be able get rid of the blocking locks in smaller pieces over time.
Tracing allows us to find the most common cause of blocking, so we
can start with the hot spots first.

The basic idea is:

btrfs_tree_lock() returns with the spin lock held

btrfs_set_lock_blocking() sets the EXTENT_BUFFER_BLOCKING bit in
the extent buffer flags, and then drops the spin lock.  The buffer is
still considered locked by all of the btrfs code.

If btrfs_tree_lock gets the spinlock but finds the blocking bit set, it drops
the spin lock and waits on a wait queue for the blocking bit to go away.

Much of the code that needs to set the blocking bit finishes without actually
blocking a good percentage of the time.  So, an adaptive spin is still
used against the blocking bit to avoid very high context switch rates.

btrfs_clear_lock_blocking() clears the blocking bit and returns
with the spinlock held again.

btrfs_tree_unlock() can be called on either blocking or spinning locks,
it does the right thing based on the blocking bit.

ctree.c has a helper function to set/clear all the locked buffers in a
path as blocking.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-02-04 09:25:08 -05:00
Chris Mason d397712bcc Btrfs: Fix checkpatch.pl warnings
There were many, most are fixed now.  struct-funcs.c generates some warnings
but these are bogus.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-01-05 21:25:51 -05:00
Chris Mason d352ac6814 Btrfs: add and improve comments
This improves the comments at the top of many functions.  It didn't
dive into the guts of functions because I was trying to
avoid merging problems with the new allocator and back reference work.

extent-tree.c and volumes.c were both skipped, and there is definitely
more work todo in cleaning and commenting the code.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2008-09-29 15:18:18 -04:00
Chris Mason 65b51a009e btrfs_search_slot: reduce lock contention by cowing in two stages
A btree block cow has two parts, the first is to allocate a destination
block and the second is to copy the old bock over.

The first part needs locks in the extent allocation tree, and may need to
do IO.  This changeset splits that into a separate function that can be
called without any tree locks held.

btrfs_search_slot is changed to drop its path and start over if it has
to COW a contended block.  This often means that many writers will
pre-alloc a new destination for a the same contended block, but they
cache their prealloc for later use on lower levels in the tree.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2008-09-25 11:04:06 -04:00
Yan bcc63abbf3 Btrfs: implement memory reclaim for leaf reference cache
The memory reclaiming issue happens when snapshot exists. In that
case, some cache entries may not be used during old snapshot dropping,
so they will remain in the cache until umount.

The patch adds a field to struct btrfs_leaf_ref to record create time. Besides,
the patch makes all dead roots of a given snapshot linked together in order of
create time. After a old snapshot was completely dropped, we check the dead
root list and remove all cache entries created before the oldest dead root in
the list.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2008-09-25 11:04:05 -04:00
Chris Mason 4881ee5a2e Btrfs: Fix some build problems on 2.6.18 based enterprise kernels
Signed-off-by: Chris Mason <chris.mason@oracle.com>
2008-09-25 11:04:05 -04:00
Chris Mason 6dddcbeb28 Btrfs: Use mutex_lock_nested for tree locking
Lockdep has the notion of locking subclasses so that you can identify
locks you expect to be taken after other locks of the same class.  This
changes the per-extent buffer btree locking routines to use a subclass based
on the level in the tree.

Unfortunately, lockdep can only handle 8 total subclasses, and the btrfs
max level is also 8.  So when lockdep is on, use a lower max level.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2008-09-25 11:04:05 -04:00
Chris Mason a61e6f29dc Btrfs: Use a mutex in the extent buffer for tree block locking
This replaces the use of the page cache lock bit for locking, which wasn't
suitable for block size < page size and couldn't be used recursively.

The mutexes alone don't fix either problem, but they are the first step.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2008-09-25 11:04:05 -04:00
Chris Mason f9efa9c784 Btrfs: Reduce contention on the root node
This calls unlock_up sooner in btrfs_search_slot in order to decrease the
amount of work done with the higher level tree locks held.

Also, it changes btrfs_tree_lock to spin for a big against the page lock
before scheduling.  This makes a big difference in context switch rate under
highly contended workloads.

Longer term, a better locking structure is needed than the page lock.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2008-09-25 11:04:04 -04:00
Chris Mason 925baeddc5 Btrfs: Start btree concurrency work.
The allocation trees and the chunk trees are serialized via their own
dedicated mutexes.  This means allocation location is still not very
fine grained.

The main FS btree is protected by locks on each block in the btree.  Locks
are taken top / down, and as processing finishes on a given level of the
tree, the lock is released after locking the lower level.

The end result of a search is now a path where only the lowest level
is locked.  Releasing or freeing the path drops any locks held.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2008-09-25 11:04:03 -04:00