We should drop dentry before deactivating the superblock, otherwise
we can hit this bug:
BUG: Dentry f349a690{i=100,n=/} still in use (1) [unmount of btrfs loop1]
...
Steps to reproduce the bug:
# mount /dev/loop1 /mnt
# mkdir save
# btrfs subvolume snapshot /mnt save/snap1
# umount /mnt
# mount -o subvol=save/snap1 /dev/loop1 /mnt
(crash)
Reported-by: Michael Niederle <mniederle@gmx.at>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
There is a problem with how we use sget, it searches through the list of supers
attached to the fs_type looking for a super with the same fs_devices as what
we're trying to mount. This depends on sb->s_fs_info being filled, but we don't
fill that in until we get to btrfs_fill_super, so we could hit supers on the
fs_type super list that have a null s_fs_info. In order to fix that we need to
go ahead and setup a blank root with a blank fs_info to hold fs_devices, that
way our test will work out right and then we can set s_fs_info in
btrfs_set_super, and then open_ctree will simply use our pre-allocated root and
fs_info when setting everything up. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
When mounting a btrfs file system btrfs_test_super() may attempt to
use sb->s_fs_info, the btrfs root, of a super block that is going away
and that has had the btrfs root set to NULL in its ->put_super(). But
if the super block is going away it cannot be an existing super block
so we can return false in this case.
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
When I added the clear_cache option I screwed up and took the break out of
the space_cache case statement, so whenever you mount with space_cache you also
get clear_cache, which does you no good if you say set space_cache in fstab so
it always gets set. This patch adds the break back in properly.
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Add a mount option user_subvol_rm_allowed that allows users to delete a
(potentially non-empty!) subvol when they would otherwise we allowed to do
an rmdir(2). We duplicate the may_delete() checks from the core VFS code
to implement identical security checks (minus the directory size check).
We additionally require that the user has write+exec permission on the
subvol root inode.
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
These are all the cases where a variable is set, but not read which are
not bugs as far as I can see, but simply leftovers.
Still needs more review.
Found by gcc 4.6's new warnings
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Use ERR_CAST(x) rather than ERR_PTR(PTR_ERR(x)). The former makes more
clear what is the purpose of the operation, which otherwise looks like a
no-op.
The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)
// <smpl>
@@
type T;
T x;
identifier f;
@@
T f (...) { <+...
- ERR_PTR(PTR_ERR(x))
+ x
...+> }
@@
expression x;
@@
- ERR_PTR(PTR_ERR(x))
+ ERR_CAST(x)
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
If something goes wrong with the free space cache we need a way to make sure
it's not loaded on mount and that it's cleared for everybody. When you pass the
clear_cache option it will make it so all block groups are setup to be cleared,
which keeps them from being loaded and then they will be truncated when the
transaction is committed. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
In order to save free space cache, we need an inode to hold the data, and we
need a special item to point at the right inode for the right block group. So
first, create a special item that will point to the right inode, and the number
of extent entries we will have and the number of bitmaps we will have. We
truncate and pre-allocate space everytime to make sure it's uptodate.
This feature will be turned on as soon as you mount with -o space_cache, however
it is safe to boot into old kernels, they will just generate the cache the old
fashion way. When you boot back into a newer kernel we will notice that we
modified and not the cache and automatically discard the cache.
Signed-off-by: Josef Bacik <josef@redhat.com>
If we failed to find the root subvol id, or the subvol=<name>, we would
deactivate the locked super and close the devices. The problem is at this point
we have gotten the SB all setup, which includes setting super_operations, so
when we'd deactiveate the super, we'd do a close_ctree() which closes the
devices, so we'd end up closing the devices twice. So if you do something like
this
mount /dev/sda1 /mnt/test1
mount /dev/sda1 /mnt/test2 -o subvol=xxx
umount /mnt/test1
it would blow up (if subvol xxx doesn't exist). This patch fixes that problem.
Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
The new ENOSPC stuff breaks out the raid types which breaks the way we were
reporting df to the system. This fixes it back so that Available is the total
space available to data and used is the actual bytes used by the filesystem.
This means that Available is Total - data used - all of the metadata space.
Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
NB: do we want btrfs_wait_ordered_range() on eviction of
inodes with positive i_nlink on subvolume with zero root_refs?
If not, btrfs_evict_inode() can be simplified by unconditionally
bailing out in case of i_nlink > 0 in the very beginning...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable:
Btrfs: The file argument for fsync() is never null
Btrfs: handle ERR_PTR from posix_acl_from_xattr()
Btrfs: avoid BUG when dropping root and reference in same transaction
Btrfs: prohibit a operation of changing acl's mask when noacl mount option used
Btrfs: should add a permission check for setfacl
Btrfs: btrfs_lookup_dir_item() can return ERR_PTR
Btrfs: btrfs_read_fs_root_no_name() returns ERR_PTRs
Btrfs: unwind after btrfs_start_transaction() errors
Btrfs: btrfs_iget() returns ERR_PTR
Btrfs: handle kzalloc() failure in open_ctree()
Btrfs: handle error returns from btrfs_lookup_dir_item()
Btrfs: Fix BUG_ON for fs converted from extN
Btrfs: Fix null dereference in relocation.c
Btrfs: fix remap_file_pages error
Btrfs: uninitialized data is check_path_shared()
Btrfs: fix fallocate regression
Btrfs: fix loop device on top of btrfs
btrfs_iget() returns an ERR_PTR() on failure and not null.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
If btrfs_lookup_dir_item() fails, we should can just let the mount fail
with an error.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable: (27 commits)
Btrfs: add more error checking to btrfs_dirty_inode
Btrfs: allow unaligned DIO
Btrfs: drop verbose enospc printk
Btrfs: Fix block generation verification race
Btrfs: fix preallocation and nodatacow checks in O_DIRECT
Btrfs: avoid ENOSPC errors in btrfs_dirty_inode
Btrfs: move O_DIRECT space reservation to btrfs_direct_IO
Btrfs: rework O_DIRECT enospc handling
Btrfs: use async helpers for DIO write checksumming
Btrfs: don't walk around with task->state != TASK_RUNNING
Btrfs: do aio_write instead of write
Btrfs: add basic DIO read/write support
direct-io: do not merge logically non-contiguous requests
direct-io: add a hook for the fs to provide its own submit_bio function
fs: allow short direct-io reads to be completed via buffered IO
Btrfs: Metadata ENOSPC handling for balance
Btrfs: Pre-allocate space for data relocation
Btrfs: Metadata ENOSPC handling for tree log
Btrfs: Metadata reservation for orphan inodes
Btrfs: Introduce global metadata reservation
...
This adds:
alias: devname:<name>
to some common kernel modules, which will allow the on-demand loading
of the kernel module when the device node is accessed.
Ideally all these modules would be compiled-in, but distros seems too
much in love with their modularization that we need to cover the common
cases with this new facility. It will allow us to remove a bunch of pretty
useless init scripts and modprobes from init scripts.
The static device node aliases will be carried in the module itself. The
program depmod will extract this information to a file in the module directory:
$ cat /lib/modules/2.6.34-00650-g537b60d-dirty/modules.devname
# Device nodes to trigger on-demand module loading.
microcode cpu/microcode c10:184
fuse fuse c10:229
ppp_generic ppp c108:0
tun net/tun c10:200
dm_mod mapper/control c10:235
Udev will pick up the depmod created file on startup and create all the
static device nodes which the kernel modules specify, so that these modules
get automatically loaded when the device node is accessed:
$ /sbin/udevd --debug
...
static_dev_create_from_modules: mknod '/dev/cpu/microcode' c10:184
static_dev_create_from_modules: mknod '/dev/fuse' c10:229
static_dev_create_from_modules: mknod '/dev/ppp' c108:0
static_dev_create_from_modules: mknod '/dev/net/tun' c10:200
static_dev_create_from_modules: mknod '/dev/mapper/control' c10:235
udev_rules_apply_static_dev_perms: chmod '/dev/net/tun' 0666
udev_rules_apply_static_dev_perms: chmod '/dev/fuse' 0666
A few device nodes are switched to statically allocated numbers, to allow
the static nodes to work. This might also useful for systems which still run
a plain static /dev, which is completely unsafe to use with any dynamic minor
numbers.
Note:
The devname aliases must be limited to the *common* and *single*instance*
device nodes, like the misc devices, and never be used for conceptually limited
systems like the loop devices, which should rather get fixed properly and get a
control node for losetup to talk to, instead of creating a random number of
device nodes in advance, regardless if they are ever used.
This facility is to hide the mess distros are creating with too modualized
kernels, and just to hide that these modules are not compiled-in, and not to
paper-over broken concepts. Thanks! :)
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Alasdair G Kergon <agk@redhat.com>
Cc: Tigran Aivazian <tigran@aivazian.fsnet.co.uk>
Cc: Ian Kent <raven@themaw.net>
Signed-Off-By: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Besides simplify the code, this change makes sure all metadata
reservation for normal metadata operations are released after
committing transaction.
Changes since V1:
Add code that check if unlink and rmdir will free space.
Add ENOSPC handling for clone ioctl.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The size of reserved space is stored in space_info. If block groups
of different raid types are linked to separate space_info, changing
allocation profile will corrupt reserved space accounting.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable:
Btrfs: add check for changed leaves in setup_leaf_for_split
Btrfs: create snapshot references in same commit as snapshot
Btrfs: fix small race with delalloc flushing waitqueue's
Btrfs: use add_to_page_cache_lru, use __page_cache_alloc
Btrfs: fix chunk allocate size calculation
Btrfs: kill max_extent mount option
Btrfs: fail to mount if we have problems reading the block groups
Btrfs: check btrfs_get_extent return for IS_ERR()
Btrfs: handle kmalloc() failure in inode lookup ioctl
Btrfs: dereferencing freed memory
Btrfs: Simplify num_stripes's calculation logical for __btrfs_alloc_chunk()
Btrfs: Add error handle for btrfs_search_slot() in btrfs_read_chunk_tree()
Btrfs: Remove unnecessary finish_wait() in wait_current_trans()
Btrfs: add NULL check for do_walk_down()
Btrfs: remove duplicate include in ioctl.c
Fix trivial conflict in fs/btrfs/compression.c due to slab.h include
cleanups.
As Yan pointed out, theres not much reason for all this complicated math to
account for file extents being split up into max_extent chunks, since they are
likely to all end up in the same leaf anyway. Since there isn't much reason to
use max_extent, just remove the option altogether so we have one less thing we
need to test.
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
percpu.h is included by sched.h and module.h and thus ends up being
included when building most .c files. percpu.h includes slab.h which
in turn includes gfp.h making everything defined by the two files
universally available and complicating inclusion dependencies.
percpu.h -> slab.h dependency is about to be removed. Prepare for
this change by updating users of gfp and slab facilities include those
headers directly instead of assuming availability. As this conversion
needs to touch large number of source files, the following script is
used as the basis of conversion.
http://userweb.kernel.org/~tj/misc/slabh-sweep.py
The script does the followings.
* Scan files for gfp and slab usages and update includes such that
only the necessary includes are there. ie. if only gfp is used,
gfp.h, if slab is used, slab.h.
* When the script inserts a new include, it looks at the include
blocks and try to put the new include such that its order conforms
to its surrounding. It's put in the include block which contains
core kernel includes, in the same order that the rest are ordered -
alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
doesn't seem to be any matching order.
* If the script can't find a place to put a new include (mostly
because the file doesn't have fitting include block), it prints out
an error message indicating which .h file needs to be added to the
file.
The conversion was done in the following steps.
1. The initial automatic conversion of all .c files updated slightly
over 4000 files, deleting around 700 includes and adding ~480 gfp.h
and ~3000 slab.h inclusions. The script emitted errors for ~400
files.
2. Each error was manually checked. Some didn't need the inclusion,
some needed manual addition while adding it to implementation .h or
embedding .c file was more appropriate for others. This step added
inclusions to around 150 files.
3. The script was run again and the output was compared to the edits
from #2 to make sure no file was left behind.
4. Several build tests were done and a couple of problems were fixed.
e.g. lib/decompress_*.c used malloc/free() wrappers around slab
APIs requiring slab.h to be added manually.
5. The script was run on all .h files but without automatically
editing them as sprinkling gfp.h and slab.h inclusions around .h
files could easily lead to inclusion dependency hell. Most gfp.h
inclusion directives were ignored as stuff from gfp.h was usually
wildly available and often used in preprocessor macros. Each
slab.h inclusion directive was examined and added manually as
necessary.
6. percpu.h was updated not to include slab.h.
7. Build test were done on the following configurations and failures
were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my
distributed build env didn't work with gcov compiles) and a few
more options had to be turned off depending on archs to make things
build (like ipr on powerpc/64 which failed due to missing writeq).
* x86 and x86_64 UP and SMP allmodconfig and a custom test config.
* powerpc and powerpc64 SMP allmodconfig
* sparc and sparc64 SMP allmodconfig
* ia64 SMP allmodconfig
* s390 SMP allmodconfig
* alpha SMP allmodconfig
* um on x86_64 SMP allmodconfig
8. percpu.h modifications were reverted so that it could be applied as
a separate patch and serve as bisection point.
Given the fact that I had only a couple of failures from tests on step
6, I'm fairly confident about the coverage of this conversion patch.
If there is a breakage, it's likely to be something in one of the arch
headers which should be easily discoverable easily on most builds of
the specific arch.
Signed-off-by: Tejun Heo <tj@kernel.org>
Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Use memparse() instead of its own private implementation.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The way we report df usage is way confusing for everybody, including some other
utilities (bacula for one). So this patch makes df a little bit more
understandable. First we make used actually count the total amount of used
space in all space info's. This will give us a real view of how much disk space
is in use. Second, for blocks available, only count data space. This makes
things like bacula work because it says 0 when you can no longer write anymore
data to the disk. I think this is a nice compromise, since you will end up with
something like the following
[root@alpha ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
148G 30G 111G 21% /
/dev/sda1 194M 116M 68M 64% /boot
tmpfs 985M 12K 985M 1% /dev/shm
/dev/mapper/VolGroup-LogVol02
145G 140G 0 100% /mnt/btrfs-test
Compare this with btrfsctl -i output
[root@alpha btrfs-progs-unstable]# ./btrfsctl -i /mnt/btrfs-test/
Metadata, DUP: total=4.62GB, used=2.46GB
System, DUP: total=8.00MB, used=24.00KB
Data: total=134.80GB, used=134.80GB
Metadata: total=8.00MB, used=0.00
System: total=4.00MB, used=0.00
operation complete
This way we show that there is no more data space to be used, but we have
another 5GB of space left for metadata. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Since theres not a good way to make sure the user sees the original default root
tree id, and not to mention it's 5 so is way different than any other volume,
just make subvol=0 mount the original default root. This makes it a bit easier
for users to handle in the long run. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This work is in preperation for being able to set a different root as the
default mounting root.
There is currently a problem with how we mount subvolumes. We cannot currently
mount a subvolume of a subvolume, you can only mount subvolumes/snapshots of the
default subvolume. So say you take a snapshot of the default subvolume and call
it snap1, and then take a snapshot of snap1 and call it snap2, so now you have
/
/snap1
/snap1/snap2
as your available volumes. Currently you can only mount / and /snap1,
you cannot mount /snap1/snap2. To fix this problem instead of passing
subvolid=<name> you must pass in subvolid=<treeid>, where <treeid> is
the tree id that gets spit out via the subvolume listing you get from
the subvolume listing patches (btrfs filesystem list). This allows us
to mount /, /snap1 and /snap1/snap2 as the root volume.
In addition to the above, we also now read the default dir item in the
tree root to get the root key that it points to. For now this just
points at what has always been the default subvolme, but later on I plan
to change it to point at whatever root you want to be the new default
root, so you can just set the default mount and not have to mount with
-o subvolid=<treeid>. I tested this out with the above scenario and it
worked perfectly. Thanks,
mount -o subvol operates inside the selected subvolid. For example:
mount -o subvol=snap1,subvolid=256 /dev/xxx /mnt
/mnt will have the snap1 directory for the subvolume with id
256.
mount -o subvol=snap /dev/xxx /mnt
/mnt will be the snap directory of whatever the default subvolume
is.
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
We kstrdup the options string, but then strsep screws with the pointer,
so when we kfree() it, we're not giving it the right pointer.
Tested-by: Andy Lutomirski <luto@mit.edu>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The default btrfs mount -o compress mode will quickly back off
compressing a file if it notices that compression does not reduce the
size of the data being written. This can save considerable CPU because
all future writes to the file go through uncompressed.
But some files are both very large and have mixed data stored in
them. In that case, we want to add the ability to always try
compressing data before writing it.
This commit adds mount -o compress-force. A later commit will add
a new inode flag that does the same thing.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Christoph's patch e244a0aeb6 doesn't display
the discard option in /proc/mounts, leading to some confusion for me.
Here's the missing bit.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
iput() can trigger new transactions if we are dropping the
final reference, so calling it in btrfs_commit_transaction
may end up deadlock. This patch adds delayed iput to avoid
the issue.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable:
Btrfs: always pin metadata in discard mode
Btrfs: enable discard support
Btrfs: add -o discard option
Btrfs: properly wait log writers during log sync
Btrfs: fix possible ENOSPC problems with truncate
Btrfs: fix btrfs acl #ifdef checks
Btrfs: streamline tree-log btree block writeout
Btrfs: avoid tree log commit when there are no changes
Btrfs: only write one super copy during fsync
Enable discard by default is not a good idea given the the trim speed
of SSD prototypes we've seen, and the carecteristics for many high-end
arrays. Turn of discards by default and require the -o discard option
to enable them on.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
The btrfs acl code was #ifdefing for a define
that didn't exist. This correctly matches it
to the values used by the Kconfig file.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
We currently set sb->s_flags |= MS_POSIXACL unconditionally, which is
incorrect -- it tells the VFS that it shouldn't set umask because we
will, yet we don't set it ourselves if we aren't using POSIX ACLs, so
the umask ends up ignored.
Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This patch adds snapshot/subvolume destroy ioctl. A subvolume that isn't being
used and doesn't contains links to other subvolumes can be destroyed.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* Remove smp_lock.h from files which don't need it (including some headers!)
* Add smp_lock.h to files which do need it
* Make smp_lock.h include conditional in hardirq.h
It's needed only for one kernel_locked() usage which is under CONFIG_PREEMPT
This will make hardirq.h inclusion cheaper for every PREEMPT=n config
(which includes allmodconfig/allyesconfig, BTW)
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Make sure a superblock really is writeable by checking MS_RDONLY
under s_umount. sync_filesystems needed some re-arragement for
that, but all but one sync_filesystem caller had the correct locking
already so that we could add that check there. cachefiles grew
s_umount locking.
I've also added a WARN_ON to sync_filesystem to assert this for
future callers.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
During mount, btrfs will check the queue nonrot flag
for all the devices found in the FS. If they are all
non-rotating, SSD mode is enabled by default.
If the FS was mounted with -o nossd, the non-rotating
flag is ignored.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
Some SSDs perform best when reusing block numbers often, while
others perform much better when clustering strictly allocates
big chunks of unused space.
The default mount -o ssd will find rough groupings of blocks
where there are a bunch of free blocks that might have some
allocated blocks mixed in.
mount -o ssd_spread will make sure there are no allocated blocks
mixed in. It should perform better on lower end SSDs.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit introduces a new kind of back reference for btrfs metadata.
Once a filesystem has been mounted with this commit, IT WILL NO LONGER
BE MOUNTABLE BY OLDER KERNELS.
When a tree block in subvolume tree is cow'd, the reference counts of all
extents it points to are increased by one. At transaction commit time,
the old root of the subvolume is recorded in a "dead root" data structure,
and the btree it points to is later walked, dropping reference counts
and freeing any blocks where the reference count goes to 0.
The increments done during cow and decrements done after commit cancel out,
and the walk is a very expensive way to go about freeing the blocks that
are no longer referenced by the new btree root. This commit reduces the
transaction overhead by avoiding the need for dead root records.
When a non-shared tree block is cow'd, we free the old block at once, and the
new block inherits old block's references. When a tree block with reference
count > 1 is cow'd, we increase the reference counts of all extents
the new block points to by one, and decrease the old block's reference count by
one.
This dead tree avoidance code removes the need to modify the reference
counts of lower level extents when a non-shared tree block is cow'd.
But we still need to update back ref for all pointers in the block.
This is because the location of the block is recorded in the back ref
item.
We can solve this by introducing a new type of back ref. The new
back ref provides information about pointer's key, level and in which
tree the pointer lives. This information allow us to find the pointer
by searching the tree. The shortcoming of the new back ref is that it
only works for pointers in tree blocks referenced by their owner trees.
This is mostly a problem for snapshots, where resolving one of these
fuzzy back references would be O(number_of_snapshots) and quite slow.
The solution used here is to use the fuzzy back references in the common
case where a given tree block is only referenced by one root,
and use the full back references when multiple roots have a reference
on a given block.
This commit adds per subvolume red-black tree to keep trace of cached
inodes. The red-black tree helps the balancing code to find cached
inodes whose inode numbers within a given range.
This commit improves the balancing code by introducing several data
structures to keep the state of balancing. The most important one
is the back ref cache. It caches how the upper level tree blocks are
referenced. This greatly reduce the overhead of checking back ref.
The improved balancing code scales significantly better with a large
number of snapshots.
This is a very large commit and was written in a number of
pieces. But, they depend heavily on the disk format change and were
squashed together to make sure git bisect didn't end up in a
bad state wrt space balancing or the format change.
Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable:
Btrfs: Spelling fix in btrfs_lookup_first_block_group comments
Btrfs: make show_options result match actual option names
Btrfs: remove outdated comment in btrfs_ioctl_resize()
Btrfs: remove some WARN_ONs in the IO failure path
Btrfs: Don't loop forever on metadata IO failures
Btrfs: init inode ordered_data_close flag properly
