This patch implements superblock duplication. Superblocks
are stored at offset 16K, 64M and 256G on every devices.
Spaces used by superblocks are preserved by the allocator,
which uses a reverse mapping function to find the logical
addresses that correspond to superblocks. Thank you,
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Shut up various sparse warnings about symbols that should be either
static or have their declarations in scope.
Signed-off-by: Christoph Hellwig <hch@lst.de>
This the lockdep complaint by having a different mutex to gaurd caching the
block group, so you don't end up with this backwards dependancy. Thank you,
Signed-off-by: Josef Bacik <jbacik@redhat.com>
The btrfs git kernel trees is used to build a standalone tree for
compiling against older kernels. This commit makes the standalone tree
work with 2.6.27
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* open/close_bdev_excl -> open/close_bdev_exclusive
* blkdev_issue_discard takes a GFP mask now
* Fix blkdev_issue_discard usage now that it is enabled
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch fixes what I hope is the last early ENOSPC bug left. I did not know
that pinned extents would merge into one big extent when inserted on to the
pinned extent tree, so I was adding free space to a block group that could
possibly span multiple block groups.
This is a big issue because first that space doesn't exist in that block group,
and second we won't actually use that space because there are a bunch of other
checks to make sure we're allocating within the constraints of the block group.
This patch fixes the problem by adding the btrfs_add_free_space to
btrfs_update_pinned_extents which makes sure we are adding the appropriate
amount of free space to the appropriate block group. Thanks much to Lee Trager
for running my myriad of debug patches to help me track this problem down.
Thank you,
Signed-off-by: Josef Bacik <jbacik@redhat.com>
In insert_extents(), when ret==1 and last is not zero, it should
check if the current inserted item is the last item in this batching
inserts. If so, it should just break from loop. If not, 'cur =
insert_list->next' will make no sense because the list is empty now,
and 'op' will point to an unexpectable place.
There are also some trivial fixs in this patch including one comment
typo error and deleting two redundant lines.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
In my batch delete/update/insert patch I introduced a free space leak. The
extent that we do the original search on in free_extents is never pinned, so we
always update the block saying that it has free space, but the free space never
actually gets added to the free space tree, since op->del will always be 0 and
it's never actually added to the pinned extents tree.
This patch fixes this problem by making sure we call pin_down_bytes on the
pending extent op and set op->del to the return value of pin_down_bytes so
update_block_group is called with the right value. This seems to fix the case
where we were getting ENOSPC when there was plenty of space available.
Signed-off-by: Josef Bacik <jbacik@redhat.com>
Seed device is a special btrfs with SEEDING super flag
set and can only be mounted in read-only mode. Seed
devices allow people to create new btrfs on top of it.
The new FS contains the same contents as the seed device,
but it can be mounted in read-write mode.
This patch does the following:
1) split code in btrfs_alloc_chunk into two parts. The first part does makes
the newly allocated chunk usable, but does not do any operation that modifies
the chunk tree. The second part does the the chunk tree modifications. This
division is for the bootstrap step of adding storage to the seed device.
2) Update device management code to handle seed device.
The basic idea is: For an FS grown from seed devices, its
seed devices are put into a list. Seed devices are
opened on demand at mounting time. If any seed device is
missing or has been changed, btrfs kernel module will
refuse to mount the FS.
3) make btrfs_find_block_group not return NULL when all
block groups are read-only.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
This patch adds mount ro and remount support. The main
changes in patch are: adding btrfs_remount and related
helper function; splitting the transaction related code
out of close_ctree into btrfs_commit_super; updating
allocator to properly handle read only block group.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
While profiling the allocator I noticed a good amount of time was being spent in
finish_current_insert and del_pending_extents, and as the filesystem filled up
more and more time was being spent in those functions. This patch aims to try
and reduce that problem. This happens two ways
1) track if we tried to delete an extent that we are going to update or insert.
Once we get into finish_current_insert we discard any of the extents that were
marked for deletion. This saves us from doing unnecessary work almost every
time finish_current_insert runs.
2) Batch insertion/updates/deletions. Instead of doing a btrfs_search_slot for
each individual extent and doing the needed operation, we instead keep the leaf
around and see if there is anything else we can do on that leaf. On the insert
case I introduced a btrfs_insert_some_items, which will take an array of keys
with an array of data_sizes and try and squeeze in as many of those keys as
possible, and then return how many keys it was able to insert. In the update
case we search for an extent ref, update the ref and then loop through the leaf
to see if any of the other refs we are looking to update are on that leaf, and
then once we are done we release the path and search for the next ref we need to
update. And finally for the deletion we try and delete the extent+ref in pairs,
so we will try to find extent+ref pairs next to the extent we are trying to free
and free them in bulk if possible.
This along with the other cluster fix that Chris pushed out a bit ago helps make
the allocator preform more uniformly as it fills up the disk. There is still a
slight drop as we fill up the disk since we start having to stick new blocks in
odd places which results in more COW's than on a empty fs, but the drop is not
nearly as severe as it was before.
Signed-off-by: Josef Bacik <jbacik@redhat.com>
When we fail to allocate a new block group, we should still do the
checks to make sure allocations try again with the minimum requested
allocation size.
This also fixes a deadlock that come from a missed down_read in
the chunk allocation failure handling.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The allocator wasn't catching all of the cases where it needed to do
extra loops because the check to enforce them wasn't happening early
enough.
When the allocator decided to increase the size of the allocation
for metadata clustering, it wasn't always setting the empty_size to
include the extra (optional) bytes. This also fixes the empty_size field
to be correct.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The loop searching for free space would exit out too soon when
metadata clustering was trying to allocate a large extent. This makes
sure a full scan of the free space is done searching for only the
minimum extent size requested by the higher layers.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
When metadata allocation clustering has to fall back to unclustered
allocs because large free areas could not be found, it was sometimes
substracting too much from the total bytes to allocate. This would
make it wrap below zero.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
In comes cases the empty cluster was added twice to the total number of
bytes the allocator was trying to find.
With empty clustering on, the hint byte was sometimes outside of the
block group. Add an extra goto to find the correct block group.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This lowers the empty cluster target for metadata allocations. The lower
target makes it easier to do allocations and still seems to perform well.
It also fixes the allocator loop to drop the empty cluster when things
start getting difficult, avoiding false enospc warnings.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The allocator uses the last allocation as a starting point for metadata
allocations, and tries to allocate in clusters of at least 256k.
If the search for a free block fails to find the expected block, this patch
forces a new cluster to be found in the free list.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
When reading compressed extents, try to put pages into the page cache
for any pages covered by the compressed extent that readpages didn't already
preload.
Add an async work queue to handle transformations at delayed allocation processing
time. Right now this is just compression. The workflow is:
1) Find offsets in the file marked for delayed allocation
2) Lock the pages
3) Lock the state bits
4) Call the async delalloc code
The async delalloc code clears the state lock bits and delalloc bits. It is
important this happens before the range goes into the work queue because
otherwise it might deadlock with other work queue items that try to lock
those extent bits.
The file pages are compressed, and if the compression doesn't work the
pages are written back directly.
An ordered work queue is used to make sure the inodes are written in the same
order that pdflush or writepages sent them down.
This changes extent_write_cache_pages to let the writepage function
update the wbc nr_written count.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch updates btrfs-progs for fallocate support.
fallocate is a little different in Btrfs because we need to tell the
COW system that a given preallocated extent doesn't need to be
cow'd as long as there are no snapshots of it. This leverages the
-o nodatacow checks.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
This patch simplifies the nodatacow checker. If all references
were created after the latest snapshot, then we can avoid COW
safely. This patch also updates run_delalloc_nocow to do more
fine-grained checking.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
When dropping middle part of an extent, btrfs_drop_extents truncates
the extent at first, then inserts a bookend extent.
Since truncation and insertion can't be done atomically, there is a small
period that the bookend extent isn't in the tree. This causes problem for
functions that search the tree for file extent item. The way to fix this is
lock the range of the bookend extent before truncation.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
finish_current_insert and del_pending_extents process extent tree modifications
that build up while we are changing the extent tree. It is a confusing
bit of code that prevents recursion.
Both functions run through a list of pending operations and both funcs
add to the list of pending operations. If you have two procs in either
one of them, they can end up looping forever making more work for each other.
This patch makes them walk forward through the list of pending changes instead
of always trying to process the entire list. At transaction commit
time, we catch any changes that were left over.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch adds transaction IDs to root tree pointers.
Transaction IDs in tree pointers are compared with the
generation numbers in block headers when reading root
blocks of trees. This can detect some types of IO errors.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
This patch removes the giant fs_info->alloc_mutex and replaces it with a bunch
of little locks.
There is now a pinned_mutex, which is used when messing with the pinned_extents
extent io tree, and the extent_ins_mutex which is used with the pending_del and
extent_ins extent io trees.
The locking for the extent tree stuff was inspired by a patch that Yan Zheng
wrote to fix a race condition, I cleaned it up some and changed the locking
around a little bit, but the idea remains the same. Basically instead of
holding the extent_ins_mutex throughout the processing of an extent on the
extent_ins or pending_del trees, we just hold it while we're searching and when
we clear the bits on those trees, and lock the extent for the duration of the
operations on the extent.
Also to keep from getting hung up waiting to lock an extent, I've added a
try_lock_extent so if we cannot lock the extent, move on to the next one in the
tree and we'll come back to that one. I have tested this heavily and it does
not appear to break anything. This has to be applied on top of my
find_free_extent redo patch.
I tested this patch on top of Yan's space reblancing code and it worked fine.
The only thing that has changed since the last version is I pulled out all my
debugging stuff, apparently I forgot to run guilt refresh before I sent the
last patch out. Thank you,
Signed-off-by: Josef Bacik <jbacik@redhat.com>
So there is an odd case where we can possibly return -ENOSPC when there is in
fact space to be had. It only happens with Metadata writes, and happens _very_
infrequently. What has to happen is we have to allocate have allocated out of
the first logical byte on the disk, which would set last_alloc to
first_logical_byte(root, 0), so search_start == orig_search_start. We then
need to allocate for normal metadata, so BTRFS_BLOCK_GROUP_METADATA |
BTRFS_BLOCK_GROUP_DUP. We will do a block lookup for the given search_start,
block_group_bits() won't match and we'll go to choose another block group.
However because search_start matches orig_search_start we go to see if we can
allocate a chunk.
If we are in the situation that we cannot allocate a chunk, we fail and ENOSPC.
This is kind of a big flaw of the way find_free_extent works, as it along with
find_free_space loop through _all_ of the block groups, not just the ones that
we want to allocate out of. This patch completely kills find_free_space and
rolls it into find_free_extent. I've introduced a sort of state machine into
this, which will make it easier to get cache miss information out of the
allocator, and will work well with my locking changes.
The basic flow is this: We have the variable loop which is 0, meaning we are
in the hint phase. We lookup the block group for the hint, and lookup the
space_info for what we want to allocate out of. If the block group we were
pointed at by the hint either isn't of the correct type, or just doesn't have
the space we need, we set head to space_info->block_groups, so we start at the
beginning of the block groups for this particular space info, and loop through.
This is also where we add the empty_cluster to total_needed. At this point
loop is set to 1 and we just loop through all of the block groups for this
particular space_info looking for the space we need, just as find_free_space
would have done, except we only hit the block groups we want and not _all_ of
the block groups. If we come full circle we see if we can allocate a chunk.
If we cannot of course we exit with -ENOSPC and we are good. If not we start
over at space_info->block_groups and loop through again, with loop == 2. If we
come full circle and haven't found what we need then we exit with -ENOSPC.
I've been running this for a couple of days now and it seems stable, and I
haven't yet hit a -ENOSPC when there was plenty of space left.
Also I've made a groups_sem to handle the group list for the space_info. This
is part of my locking changes, but is relatively safe and seems better than
holding the space_info spinlock over that entire search time. Thanks,
Signed-off-by: Josef Bacik <jbacik@redhat.com>
This patch improves the space balancing code to keep more sharing
of tree blocks. The only case that breaks sharing of tree blocks is
data extents get fragmented during balancing. The main changes in
this patch are:
Add a 'drop sub-tree' function. This solves the problem in old code
that BTRFS_HEADER_FLAG_WRITTEN check breaks sharing of tree block.
Remove relocation mapping tree. Relocation mappings are stored in
struct btrfs_ref_path and updated dynamically during walking up/down
the reference path. This reduces CPU usage and simplifies code.
This patch also fixes a bug. Root items for reloc trees should be
updated in btrfs_free_reloc_root.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
This is a large change for adding compression on reading and writing,
both for inline and regular extents. It does some fairly large
surgery to the writeback paths.
Compression is off by default and enabled by mount -o compress. Even
when the -o compress mount option is not used, it is possible to read
compressed extents off the disk.
If compression for a given set of pages fails to make them smaller, the
file is flagged to avoid future compression attempts later.
* While finding delalloc extents, the pages are locked before being sent down
to the delalloc handler. This allows the delalloc handler to do complex things
such as cleaning the pages, marking them writeback and starting IO on their
behalf.
* Inline extents are inserted at delalloc time now. This allows us to compress
the data before inserting the inline extent, and it allows us to insert
an inline extent that spans multiple pages.
* All of the in-memory extent representations (extent_map.c, ordered-data.c etc)
are changed to record both an in-memory size and an on disk size, as well
as a flag for compression.
From a disk format point of view, the extent pointers in the file are changed
to record the on disk size of a given extent and some encoding flags.
Space in the disk format is allocated for compression encoding, as well
as encryption and a generic 'other' field. Neither the encryption or the
'other' field are currently used.
In order to limit the amount of data read for a single random read in the
file, the size of a compressed extent is limited to 128k. This is a
software only limit, the disk format supports u64 sized compressed extents.
In order to limit the ram consumed while processing extents, the uncompressed
size of a compressed extent is limited to 256k. This is a software only limit
and will be subject to tuning later.
Checksumming is still done on compressed extents, and it is done on the
uncompressed version of the data. This way additional encodings can be
layered on without having to figure out which encoding to checksum.
Compression happens at delalloc time, which is basically singled threaded because
it is usually done by a single pdflush thread. This makes it tricky to
spread the compression load across all the cpus on the box. We'll have to
look at parallel pdflush walks of dirty inodes at a later time.
Decompression is hooked into readpages and it does spread across CPUs nicely.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Due to the optimization for truncate, tree leaves only containing
checksum items can be deleted without being COW'ed first. This causes
reference cache misses. The way to fix the miss is create cache
entries for tree leaves only contain checksum.
This patch also fixes a -EEXIST issue in shared reference cache.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
The offset field in struct btrfs_extent_ref records the position
inside file that file extent is referenced by. In the new back
reference system, tree leaves holding references to file extent
are recorded explicitly. We can scan these tree leaves very quickly, so the
offset field is not required.
This patch also makes the back reference system check the objectid
when extents are in deleting.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
This patch makes btrfs count space allocated to file in bytes instead
of 512 byte sectors.
Everything else in btrfs uses a byte count instead of sector sizes or
blocks sizes, so this fits better.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
The tree logging code was trying to separate tree log allocations
from normal metadata allocations to improve writeback patterns during
an fsync.
But, the code was not effective and ended up just mixing tree log
blocks with regular metadata. That seems to be working fairly well,
so the last_log_alloc code can be removed.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This fixes a deadlock that happens between the alloc_mutex and chunk_mutex.
Process A comes in, decides to do a do_chunk_alloc, which takes the
chunk_mutex, and is holding the alloc_mutex because the only way you get to
do_chunk_alloc is by holding the alloc_mutex. btrfs_alloc_chunk does its thing
and goes to insert a new item, which results in a cow of the block.
We get into del_pending_extents from there, where if we need to be rescheduled
we drop the alloc_mutex and schedule. At this point process B comes in to do
an allocation and gets the alloc_mutex, and because process A did not do the
chunk allocation completely it thinks its a good time to do a chunk allocation
as well, and hangs on the chunk_mutex.
Process A wakes up and tries to take the alloc_mutex and cannot. The way to
fix this is do a mutex_trylock() on chunk_mutex. If we return 0 we didn't get
the lock, and if this is just a "hey it may be a good time to allocate a chunk"
then we just exit. If we are trying to force an allocation then we reschedule
and keep trying to acquire the chunk_mutex. If once we acquire it the space is
already full then we can just exit, otherwise we can continue with the chunk
allocation. Thank you,
Signed-off-by: Josef Bacik <jbacik@redhat.com>
When reading in block groups, a global mask of the available raid policies
should be adjusted based on the types of block groups found on disk. This
global mask is then used to decide which raid policy to use for new
block groups.
The recent allocator changes dropped the call that updated the global
mask, making all the block groups allocated at run time single striped
onto a single drive.
This also fixes the async worker threads to set any thread that uses
the requeue mechanism as busy. This allows us to avoid blocking
on get_request_wait for the async bio submission threads.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch fixes a problem where we end up seeking too much when *last_ptr is
valid. This happens because btrfs_lookup_first_block_group only returns a
block group that starts on or after the given search start, so if the
search_start is in the middle of a block group it will return the block group
after the given search_start, which is suboptimal.
This patch fixes that by doing a btrfs_lookup_block_group, which will return
the block group that contains the given search start. If we fail to find a
block group, we fall back on btrfs_lookup_first_block_group so we can find the
next block group, not sure if this is absolutely needed, but better safe than
sorry.
Also if we can't find the block group that we need, or it happens to not be of
the right type, we need to add empty_cluster since *last_ptr could point to a
mismatched block group, which means we need to start over with empty_cluster
added to total needed. Thank you,
Signed-off-by: Josef Bacik <jbacik@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch updates the space balancing code to utilize the new
backref format. Before, btrfs-vol -b would break any COW links
on data blocks or metadata. This was slow and caused the amount
of space used to explode if a large number of snapshots were present.
The new code can keeps the sharing of all data extents and
most of the tree blocks.
To maintain the sharing of data extents, the space balance code uses
a seperate inode hold data extent pointers, then updates the references
to point to the new location.
To maintain the sharing of tree blocks, the space balance code uses
reloc trees to relocate tree blocks in reference counted roots.
There is one reloc tree for each subvol, and all reloc trees share
same root key objectid. Reloc trees are snapshots of the latest
committed roots of subvols (root->commit_root).
To relocate a tree block referenced by a subvol, there are two steps.
COW the block through subvol's reloc tree, then update block pointer in
the subvol to point to the new block. Since all reloc trees share
same root key objectid, doing special handing for tree blocks
owned by them is easy. Once a tree block has been COWed in one
reloc tree, we can use the resulting new block directly when the
same block is required to COW again through other reloc trees.
In this way, relocated tree blocks are shared between reloc trees,
so they are also shared between subvols.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Btrfs has a cache of reference counts in leaves, allowing it to
avoid reading tree leaves while deleting snapshots. To reduce
contention with multiple subvolumes, this cache is private to each
subvolume.
This patch adds shared reference cache support. The new space
balancing code plays with multiple subvols at the same time, So
the old per-subvol reference cache is not well suited.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* Reserved extent accounting: reserved extents have been
allocated in the rbtrees that track free space but have not
been allocated on disk. They were never properly accounted for
in the past, making it hard to know how much space was really free.
* btrfs_find_block_group used to return NULL for block groups that
had been removed by the space balancing code. This made it hard
to account for space during the final stages of a balance run.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The code to free block groups needs to drop the space info spin lock
before calling btrfs_remove_free_space_cache (which can schedule).
This is safe because at unmount time, nobody else is going to play
with the block groups.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch makes the back reference system to explicit record the
location of parent node for all types of extents. The location of
parent node is placed into the offset field of backref key. Every
time a tree block is balanced, the back references for the affected
lower level extents are updated.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Tree log blocks are only reserved, and should not ever get fully
allocated on disk. This check makes sure they stay out of the
extent tree.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
1) replace the per fs_info extent_io_tree that tracked free space with two
rb-trees per block group to track free space areas via offset and size. The
reason to do this is because most allocations come with a hint byte where to
start, so we can usually find a chunk of free space at that hint byte to satisfy
the allocation and get good space packing. If we cannot find free space at or
after the given offset we fall back on looking for a chunk of the given size as
close to that given offset as possible. When we fall back on the size search we
also try to find a slot as close to the size we want as possible, to avoid
breaking small chunks off of huge areas if possible.
2) remove the extent_io_tree that tracked the block group cache from fs_info and
replaced it with an rb-tree thats tracks block group cache via offset. also
added a per space_info list that tracks the block group cache for the particular
space so we can lookup related block groups easily.
3) cleaned up the allocation code to make it a little easier to read and a
little less complicated. Basically there are 3 steps, first look from our
provided hint. If we couldn't find from that given hint, start back at our
original search start and look for space from there. If that fails try to
allocate space if we can and start looking again. If not we're screwed and need
to start over again.
4) small fixes. there were some issues in volumes.c where we wouldn't allocate
the rest of the disk. fixed cow_file_range to actually pass the alloc_hint,
which has helped a good bit in making the fs_mark test I run have semi-normal
results as we run out of space. Generally with data allocations we don't track
where we last allocated from, so everytime we did a data allocation we'd search
through every block group that we have looking for free space. Now searching a
block group with no free space isn't terribly time consuming, it was causing a
slight degradation as we got more data block groups. The alloc_hint has fixed
this slight degredation and made things semi-normal.
There is still one nagging problem I'm working on where we will get ENOSPC when
there is definitely plenty of space. This only happens with metadata
allocations, and only when we are almost full. So you generally hit the 85%
mark first, but sometimes you'll hit the BUG before you hit the 85% wall. I'm
still tracking it down, but until then this seems to be pretty stable and make a
significant performance gain.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
cache block group had a few bugs in the error handling code,
this makes sure paths get properly released and the correct return value
goes out.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This is the same way the transaction code makes sure that all the
other tree blocks are safely on disk. There's an extent_io tree
for each root, and any blocks allocated to the tree logs are
recorded in that tree.
At tree-log sync, the extent_io tree is walked to flush down the
dirty pages and wait for them.
The main benefit is less time spent walking the tree log and skipping
clean pages, and getting sequential IO down to the drive.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Since tree log blocks get freed every transaction, they never really
need to be written to disk. This skips the step where we update
metadata to record they were allocated.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* Pin down data blocks to prevent them from being reallocated like so:
trans 1: allocate file extent
trans 2: free file extent
trans 3: free file extent during old snapshot deletion
trans 3: allocate file extent to new file
trans 3: fsync new file
Before the tree logging code, this was legal because the fsync
would commit the transation that did the final data extent free
and the transaction that allocated the extent to the new file
at the same time.
With the tree logging code, the tree log subtransaction can commit
before the transaction that freed the extent. If we crash,
we're left with two different files using the extent.
* Don't wait in start_transaction if log replay is going on. This
avoids deadlocks from iput while we're cleaning up link counts in the
replay code.
* Don't deadlock in replay_one_name by trying to read an inode off
the disk while holding paths for the directory
* Hold the buffer lock while we mark a buffer as written. This
closes a race where someone is changing a buffer while we write it.
They are supposed to mark it dirty again after they change it, but
this violates the cow rules.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
File syncs and directory syncs are optimized by copying their
items into a special (copy-on-write) log tree. There is one log tree per
subvolume and the btrfs super block points to a tree of log tree roots.
After a crash, items are copied out of the log tree and back into the
subvolume. See tree-log.c for all the details.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
