While dropping snapshots, walk_down_tree does most of the work of checking
reference counts and limiting tree traversal to just the blocks that
we are freeing.
It dropped and held the allocation mutex in strange and confusing ways,
this commit changes it to only hold the mutex while actually freeing a block.
The rest of the checks around reference counts should be safe without the lock
because we only allow one process in btrfs_drop_snapshot at a time. Other
processes dropping reference counts should not drop it to 1 because
their tree roots already have an extra ref on the block.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This avoids waiting for transactions with pages locked by breaking out
the code to wait for the current transaction to close into a function
called by btrfs_throttle.
It also lowers the limits for where we start throttling.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
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>
To check whether a given file extent is referenced by multiple snapshots, the
checker walks down the fs tree through dead root and checks all tree blocks in
the path.
We can easily detect whether a given tree block is directly referenced by other
snapshot. We can also detect any indirect reference from other snapshot by
checking reference's generation. The checker can always detect multiple
references, but can't reliably detect cases of single reference. So btrfs may
do file data cow even there is only one reference.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
A large reference cache is directly related to a lot of work pending
for the cleaner thread. This throttles back new operations based on
the size of the reference cache so the cleaner thread will be able to keep
up.
Overall, this actually makes the FS faster because the cleaner thread will
be more likely to find things in cache.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This changes the reference cache to make a single cache per root
instead of one cache per transaction, and to key by the byte number
of the disk block instead of the keys inside.
This makes it much less likely to have cache misses if a snapshot
or something has an extra reference on a higher node or a leaf while
the first transaction that added the leaf into the cache is dropping.
Some throttling is added to functions that free blocks heavily so they
wait for old transactions to drop.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Much of the IO done while dropping snapshots is done looking up
leaves in the filesystem trees to see if they point to any extents and
to drop the references on any extents found.
This creates a cache so that IO isn't required.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Before setting an extent to delalloc, the code needs to wait for
pending ordered extents.
Also, the relocation code needs to wait for ordered IO before scanning
the block group again. This is because the extents are not removed
until the IO for the new extents is finished
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This releases the alloc_mutex in a few places that hold it for over long
operations. btrfs_lookup_block_group is changed so that it doesn't need
the mutex at all.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
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>
* In btrfs_delete_inode, wait for ordered extents after calling
truncate_inode_pages. This is much faster, and more correct
* Properly clear our the PageChecked bit everywhere we redirty the page.
* Change the writepage fixup handler to lock the page range and check to
see if an ordered extent had been inserted since the improperly dirtied
page was discovered
* Wait for ordered extents outside the transaction. This isn't required
for locking rules but does improve transaction latencies
* Reduce contention on the alloc_mutex by dropping it while incrementing
refs on a node/leaf and while dropping refs on a leaf.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
btrfs_drop_extents is always called with a range lock held on the inode.
But, it may operate on extents outside that range as it drops and splits
them.
This patch adds a per-inode mutex that is held while calling
btrfs_drop_extents and while inserting new extents into the tree. It
prevents races from two procs working against adjacent ranges in the tree.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The old data=ordered code would force commit to wait until
all the data extents from the transaction were fully on disk. This
introduced large latencies into the commit and stalled new writers
in the transaction for a long time.
The new code changes the way data allocations and extents work:
* When delayed allocation is filled, data extents are reserved, and
the extent bit EXTENT_ORDERED is set on the entire range of the extent.
A struct btrfs_ordered_extent is allocated an inserted into a per-inode
rbtree to track the pending extents.
* As each page is written EXTENT_ORDERED is cleared on the bytes corresponding
to that page.
* When all of the bytes corresponding to a single struct btrfs_ordered_extent
are written, The previously reserved extent is inserted into the FS
btree and into the extent allocation trees. The checksums for the file
data are also updated.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The btree defragger wasn't making forward progress because the new key wasn't
being saved by the btrfs_search_forward function.
This also disables the automatic btree defrag, it wasn't scaling well to
huge filesystems. The auto-defrag needs to be done differently.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This makes it possible for callers to check for extent_buffers in cache
without deadlocking against any btree locks held.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The online btree defragger is simplified and rewritten to use
standard btree searches instead of a walk up / down mechanism.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This creates one kthread for commits and one kthread for
deleting old snapshots. All the work queues are removed.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Allocations may need to read in block groups from the extent allocation tree,
which will require a tree search and take locks on the extent allocation
tree. But, those locks might already be held in other places, leading
to deadlocks.
Since the alloc_mutex serializes everything right now, it is safe to
skip the btree locking while caching block groups. A better fix will be
to either create a recursive lock or find a way to back off existing
locks while caching block groups.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
One lock per btree block can make for significant congestion if everyone
has to wait for IO at the high levels of the btree. This drops
locks held by a path when doing reads during a tree search.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Extent alloctions are still protected by a large alloc_mutex.
Objectid allocations are covered by a objectid mutex
Other btree operations are protected by a lock on individual btree nodes
Signed-off-by: Chris Mason <chris.mason@oracle.com>
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>
* Force chunk allocation when find_free_extent has to do a full scan
* Record the max key at the start of defrag so it doesn't run forever
* Block groups might not be contiguous, make a forward search for the
next block group in extent-tree.c
* Get rid of extra checks for total fs size
* Fix relocate_one_reference to avoid relocating the same file data block
twice when referenced by an older transaction
* Use the open device count when allocating chunks so that we don't
try to allocate from devices that don't exist
Signed-off-by: Chris Mason <chris.mason@oracle.com>
When duplicate copies exist, writes are allowed to fail to one of those
copies. This changeset includes a few changes that allow the FS to
continue even when some IOs fail.
It also adds verification of the parent generation number for btree blocks.
This generation is stored in the pointer to a block, and it ensures
that missed writes to are detected.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Once part of a delalloc request fails the cow checks, just cow the
entire range
It is possible for the back references to all be from the same root,
but still have snapshots against an extent. The checks are now more strict,
forcing cow any time there are multiple refs against the data extent.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Before, nodatacow only checked to make sure multiple roots didn't have
references on a single extent. This check makes sure that multiple
inodes don't have references.
nodatacow needed an extra check to see if the block group was currently
readonly. This way cows forced by the chunk relocation code are honored.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This required a few structural changes to the code that manages bdev pointers:
The VFS super block now gets an anon-bdev instead of a pointer to the
lowest bdev. This allows us to avoid swapping the super block bdev pointer
around at run time.
The code to read in the super block no longer goes through the extent
buffer interface. Things got ugly keeping the mapping constant.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
balance level starts by trying to empty the middle block, and then
pushes from the right to the middle. This might empty the right block
and leave a small number of pointers in the middle.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The data read retry code needs to find the logical disk block before it
can resubmit new bios. But, finding this block isn't allowed to take
the fs_mutex because that will deadlock with a number of different callers.
This changes the retry code to use the extent map cache instead, but
that requires the extent map cache to have the extent we're looking for.
This is a problem because btrfs_drop_extent_cache just drops the entire
extent instead of the little tiny part it is invalidating.
The bulk of the code in this patch changes btrfs_drop_extent_cache to
invalidate only a portion of the extent cache, and changes btrfs_get_extent
to deal with the results.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This isn't required anymore because we don't reallocate blocks that
have already been written in this transaction.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Block headers now store the chunk tree uuid
Chunk items records the device uuid for each stripes
Device extent items record better back refs to the chunk tree
Block groups record better back refs to the chunk tree
The chunk tree format has also changed. The objectid of BTRFS_CHUNK_ITEM_KEY
used to be the logical offset of the chunk. Now it is a chunk tree id,
with the logical offset being stored in the offset field of the key.
This allows a single chunk tree to record multiple logical address spaces,
upping the number of bytes indexed by a chunk tree from 2^64 to
2^128.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
On huge machines, delayed allocation may try to allocate massive extents.
This change allows btrfs_alloc_extent to return something smaller than
the caller asked for, and the data allocation routines will loop over
the allocations until it fills the whole delayed alloc.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Fix for a endianess BUG when using btrfs v0.13 with kernels older than 2.6.23
Problem:
Has of v0.13, btrfs-progs is using crc32c.c equivalent to the one found on
linux-2.6.23/lib/libcrc32c.c Since crc32c_le() changed in linux-2.6.23, when
running btrfs v0.13 with older kernels we have a missmatch between the versions
of crc32c_le() from btrfs-progs and libcrc32c in the kernel. This missmatch
causes a bug when using btrfs on big endian machines.
Solution:
btrfs_crc32c() macro that when compiling for kernels older than 2.6.23, does
endianess conversion to parameters and return value of crc32c().
This endianess conversion nullifies the differences in implementation
of crc32c_le().
If kernel 2.6.23 or better, it calls crc32c().
Signed-off-by: Miguel Sousa Filipe <miguel.filipe@gmail.com>
---
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Before, metadata checksumming was done by the callers of read_tree_block,
which would set EXTENT_CSUM bits in the extent tree to show that a given
range of pages was already checksummed and didn't need to be verified
again.
But, those bits could go away via try_to_releasepage, and the end
result was bogus checksum failures on pages that never left the cache.
The new code validates checksums when the page is read. It is a little
tricky because metadata blocks can span pages and a single read may
end up going via multiple bios.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
When a block is freed, it can be immediately reused if it is from
the current transaction. But, an extra check is required to make sure
the block had not been written yet. If it were reused after being written,
the transid in the block header might match the transid of the
next time the block was allocated.
The parent node records the transaction ID of the block it is pointing to,
and this is used as part of validating the block on reads. So, there
can only be one version of a block per transaction.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Checksums were only verified by btrfs_read_tree_block, which meant the
functions to probe the page cache for blocks were not validating checksums.
Normally this is fine because the buffers will only be in cache if they
have already been validated.
But, there is a window while the buffer is being read from disk where
it could be up to date in the cache but not yet verified. This patch
makes sure all buffers go through checksum verification before they
are used.
This is safer, and it prevents modification of buffers before they go
through the csum code.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
There was an optimization to drop the fs_mutex when doing snapshot deletion
reads, but this can lead to false positives on checksumming errors. Keep
the lock for now.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Reduce CPU time searching for free blocks by optimizing find_first_extent_bit
Fix find_free_extent to make better use of the last_alloc hint. Before it
was often finding blocks just before the hint.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This makes searches for backrefs and backref insertion much more efficient
when there are many backrefs for a single extent
Signed-off-by: Chris Mason <chris.mason@oracle.com>
There is now extent_map for mapping offsets in the file to disk and
extent_io for state tracking, IO submission and extent_bufers.
The new extent_map code shifts from [start,end] pairs to [start,len], and
pushes the locking out into the caller. This allows a few performance
optimizations and is easier to use.
A number of extent_map usage bugs were fixed, mostly with failing
to remove extent_map entries when changing the file.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
While shrinking the FS, the allocation functions need to make sure
they don't try to allocate bytes past the end of the FS.
nodatacow needed an extra check to force cows when the existing extents are
past the end of the FS.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This forces file data extents down the disk along with the metadata that
references them. The current implementation is fairly simple, and just
writes out all of the dirty pages in an inode before the commit.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The shrinking code used btrfs_next_leaf to find the next item, but
this does not cow the blocks it touches. This fix calls search_slot after
finding the next item to do appropriate cow and balancing.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The patch fixes the overlapping extent issue in shrink_extent_tree.
It checks whether there is an overlapping extent by using
find_previous_extent. If there is an overlapping extent, it setups
key.objectid and cur_byte properly.
---
Signed-off-by: Chris Mason <chris.mason@oracle.com>
A number of workloads do not require copy on write data or checksumming.
mount -o nodatasum to disable checksums and -o nodatacow to disable
both copy on write and checksumming.
In nodatacow mode, copy on write is still performed when a given extent
is under snapshot.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch adds a new parameter 'full_scan' to 'find_search_start',
thereby 'find_search_start' can know whether 'find_free_extent' is in
full scan phrase. I feel that 'find_search_start' should skip calling
'btrfs_find_block_group' when 'find_free_extent' is in full scan
phrase. In my test on a 2GB volume, Oops occurs when space usage is
about 76%. After apply the patch, Oops occurs when space usage is
near 100%.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch adds a helper function 'update_pinned_extents' to
extent-tree.c. The usage of the helper function is similar to
'update_block_group', the last parameter of the function indicates
pin vs unpin.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
When pin_down_bytes decides not to pin a block because it was from the
current transaction, make sure the in memory cache of free extents is updated
Signed-off-by: Chris Mason <chris.mason@oracle.com>
find_free_extent would fail to wrap around to the start of the drive because
it was doing the enospc case checking twice in some cases, causing it
to return -ENOSPC early.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
btrfs_btree_balance_dirty is changed to pass the number of pages dirtied
for more accurate dirty throttling. This lets the VM make better decisions
about when to force some writeback.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Cache block group was overly complex and missed free blocks at the very start
of the group. This patch simplifies things significantly.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This allows the tree walking code to defrag only the newly allocated
buffers, it seems to be a good balance between perfect defragging and the
performance hit of repeatedly reallocating blocks.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This adds two types of btree defrag, a run time form that tries to
defrag recently allocated blocks in the btree when they are still in ram,
and an ioctl that forces defrag of all btree blocks.
File data blocks are not defragged yet, but this can make a huge difference
in sequential btree reads.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Before, snapshot deletion was a single atomic unit. This caused considerable
lock contention and required an unbounded amount of space. Now,
the drop_progress field in the root item is used to indicate how far along
snapshot deletion is, and to resume where it left off.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Almost none of the files including module.h need to do so,
remove them.
Include sched.h in extent-tree.c to silence a warning about cond_resched()
being undeclared.
Signed-off-by: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The super block written during commit was not consistent with the state of
the trees. This change adds an in-memory copy of the super so that we can
make sure to write out consistent data during a commit.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Attaching below is some of the code cleanups that i came across while
reading the code.
a) alloc_path already calls init_path.
b) Mention that btrfs_inode is the in memory copy.Ext4 have ext4_inode_info as
the in memory copy ext4_inode as the disk copy
Signed-off-by: Chris Mason <chris.mason@oracle.com>
