Writing a large file using direct IO in 16 MB chunks sometimes results
in a pathological allocation pattern where 16 MB chunks of large free
extent are allocated to a file in a reversed order. So extents of a file
look for example as:
ext logical physical expected length flags
0 0 13 4550656
1 4550656 188136807 4550668 12562432
2 17113088 200699240 200699238 622592
3 17735680 182046055 201321831 4096
4 17739776 182041959 182050150 4096
5 17743872 182037863 182046054 4096
6 17747968 182033767 182041958 4096
7 17752064 182029671 182037862 4096
...
6757 45400064 154381644 154389835 4096
6758 45404160 154377548 154385739 4096
6759 45408256 252951571 154381643 73728 eof
This happens because XFS_ALLOCTYPE_THIS_BNO allocation fails (the last
extent in the file cannot be further extended) so we fall back to
XFS_ALLOCTYPE_NEAR_BNO allocation which picks end of a large free
extent as the best place to continue the file. Since the chunk at the
end of the free extent again cannot be further extended, this behavior
repeats until the whole free extent is consumed in a reversed order.
For data allocations this backward allocation isn't beneficial so make
xfs_alloc_compute_diff() pick start of a free extent instead of its end
for them. That avoids the backward allocation pattern.
See thread at http://oss.sgi.com/archives/xfs/2013-03/msg00144.html for
more details about the reproduction case and why this solution was
chosen.
Based on idea by Dave Chinner <dchinner@redhat.com>.
CC: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
The buffer type passed to log recvoery in the buffer log item
overruns the blf_flags field. I had assumed that flags field was a
32 bit value, and it turns out it is a unisgned short. Therefore
having 19 flags doesn't really work.
Convert the buffer type field to numeric value, and use the top 5
bits of the flags field for it. We currently have 17 types of
buffers, so using 5 bits gives us plenty of room for expansion in
future....
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Add CRC checks, location information and a magic number to the AGFL.
Previously the AGFL was just a block containing nothing but the
free block pointers. The new AGFL has a real header with the usual
boilerplate instead, so that we can verify it's not corrupted and
written into the right place.
[dchinner@redhat.com] Added LSN field, reworked significantly to fit
into new verifier structure and growfs structure, enabled full
verifier functionality now there is a header to verify and we can
guarantee an initialised AGFL.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
The AGF already has some self identifying fields (e.g. the sequence
number) so we only need to add the uuid to it to identify the
filesystem it belongs to. The location is fixed based on the
sequence number, so there's no need to add a block number, either.
Hence the only additional fields are the CRC and LSN fields. These
are unlogged, so place some space between the end of the logged
fields and them so that future expansion of the AGF for logged
fields can be placed adjacent to the existing logged fields and
hence not complicate the field-derived range based logging we
currently have.
Based originally on a patch from myself, modified further by
Christoph Hellwig and then modified again to fit into the
verifier structure with additional fields by myself. The multiple
signed-off-by tags indicate the age and history of this patch.
Signed-off-by: Dave Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Use more preferable function name which implies using a pseudo-random
number generator.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: <bpm@sgi.com>
Cc: Ben Myers <bpm@sgi.com>
Cc: Alex Elder <elder@kernel.org>
Cc: xfs@oss.sgi.com
Signed-off-by: Ben Myers <bpm@sgi.com>
Commit 408cc4e97a
added memset(0, ...) to allocation args structures,
so there is no need to explicitly set any of the fields
to 0 after that.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
To separate the verifiers from iodone functions and associate read
and write verifiers at the same time, introduce a buffer verifier
operations structure to the xfs_buf.
This avoids the need for assigning the write verifier, clearing the
iodone function and re-running ioend processing in the read
verifier, and gets rid of the nasty "b_pre_io" name for the write
verifier function pointer. If we ever need to, it will also be
easier to add further content specific callbacks to a buffer with an
ops structure in place.
We also avoid needing to export verifier functions, instead we
can simply export the ops structures for those that are needed
outside the function they are defined in.
This patch also fixes a directory block readahead verifier issue
it exposed.
This patch also adds ops callbacks to the inode/alloc btree blocks
initialised by growfs. These will need more work before they will
work with CRCs.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Phil White <pwhite@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Metadata buffers that are read from disk have write verifiers
already attached to them, but newly allocated buffers do not. Add
appropriate write verifiers to all new metadata buffers.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
These verifiers are essentially the same code as the read verifiers,
but do not require ioend processing. Hence factor the read verifier
functions and add a new write verifier wrapper that is used as the
callback.
This is done as one large patch for all verifiers rather than one
patch per verifier as the change is largely mechanical. This
includes hooking up the write verifier via the read verifier
function.
Hooking up the write verifier for buffers obtained via
xfs_trans_get_buf() will be done in a separate patch as that touches
code in many different places rather than just the verifier
functions.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Add an AGFL block verify callback function and pass it into the
buffer read functions.
While this commit adds verification code to the AGFL, it cannot be
used reliably until the CRC format change comes along as mkfs does
not initialise the full AGFL. Hence it can be full of garbage at the
first mount and will fail verification right now. CRC enabled
filesystems won't have this problem, so leave the code that has
already been written ifdef'd out until the proper time.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Phil White <pwhite@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Add an AGF block verify callback function and pass it into the
buffer read functions. This replaces the existing verification that
is done after the read completes.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Add a verifier function callback capability to the buffer read
interfaces. This will be used by the callers to supply a function
that verifies the contents of the buffer when it is read from disk.
This patch does not provide callback functions, but simply modifies
the interfaces to allow them to be called.
The reason for adding this to the read interfaces is that it is very
difficult to tell fom the outside is a buffer was just read from
disk or whether we just pulled it out of cache. Supplying a callbck
allows the buffer cache to use it's internal knowledge of the buffer
to execute it only when the buffer is read from disk.
It is intended that the verifier functions will mark the buffer with
an EFSCORRUPTED error when verification fails. This allows the
reading context to distinguish a verification error from an IO
error, and potentially take further actions on the buffer (e.g.
attempt repair) based on the error reported.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Phil White <pwhite@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Switching stacks are xfs_alloc_vextent can cause deadlocks when we
run out of worker threads on the allocation workqueue. This can
occur because xfs_bmap_btalloc can make multiple calls to
xfs_alloc_vextent() and even if xfs_alloc_vextent() fails it can
return with the AGF locked in the current allocation transaction.
If we then need to make another allocation, and all the allocation
worker contexts are exhausted because the are blocked waiting for
the AGF lock, holder of the AGF cannot get it's xfs-alloc_vextent
work completed to release the AGF. Hence allocation effectively
deadlocks.
To avoid this, move the stack switch one layer up to
xfs_bmapi_allocate() so that all of the allocation attempts in a
single switched stack transaction occur in a single worker context.
This avoids the problem of an allocation being blocked waiting for
a worker thread whilst holding the AGF.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Certain allocation paths through xfs_bmapi_write() are in situations
where we have limited stack available. These are almost always in
the buffered IO writeback path when convertion delayed allocation
extents to real extents.
The current stack switch occurs for userdata allocations, which
means we also do stack switches for preallocation, direct IO and
unwritten extent conversion, even those these call chains have never
been implicated in a stack overrun.
Hence, let's target just the single stack overun offended for stack
switches. To do that, introduce a XFS_BMAPI_STACK_SWITCH flag that
the caller can pass xfs_bmapi_write() to indicate it should switch
stacks if it needs to do allocation.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Zero the kernel stack space that makes up the xfs_alloc_arg structures.
Signed-off-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Almost all metadata allocations come from shallow stack usage
situations. Avoid the overhead of switching the allocation to a
workqueue as we are not in danger of running out of stack when
making these allocations. Metadata allocations are already marked
through the args that are passed down, so this is trivial to do.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reported-by: Mel Gorman <mgorman@suse.de>
Tested-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Ben Myers <bpm@sgi.com>
The current cursor is reallocated when retrying the allocation, so
the existing cursor needs to be destroyed in both the restart and
the failure cases.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Tested-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
When we fail to find an matching extent near the requested extent
specification during a left-right distance search in
xfs_alloc_ag_vextent_near, we fail to free the original cursor that
we used to look up the XFS_BTNUM_CNT tree and hence leak it.
Reported-by: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>
Commit e459df5, 'xfs: move busy extent handling to it's own file'
moved some code from xfs_alloc.c into xfs_extent_busy.c for
convenience in userspace code merges. One of the functions moved is
xfs_extent_busy_trim (formerly xfs_alloc_busy_trim) which is defined
STATIC. Unfortunately this function is still used in xfs_alloc.c, and
this results in an undefined symbol in xfs.ko.
Make xfs_extent_busy_trim not static and add its prototype to
xfs_extent_busy.h.
Signed-off-by: Ben Myers <bpm@sgi.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Now that the busy extent tracking has been moved out of the
allocation files, clean up the namespace it uses to
"xfs_extent_busy" rather than a mix of "xfs_busy" and
"xfs_alloc_busy".
Signed-off-by: Dave Chinner<dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
To make it easier to handle userspace code merges, move all the busy
extent handling out of the allocation code and into it's own file.
The userspace code does not need the busy extent code, so this
simplifies the merging of the kernel code into the userspace
xfsprogs library.
Because the busy extent code has been almost completely rewritten
over the past couple of years, also update the copyright on this new
file to include the authors that made all those changes.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Untangle the header file includes a bit by moving the definition of
xfs_agino_t to xfs_types.h. This removes the dependency that xfs_ag.h has on
xfs_inum.h, meaning we don't need to include xfs_inum.h everywhere we include
xfs_ag.h.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
xfs_ioc_fstrim() doesn't treat the incoming offset and length
correctly. It treats them as a filesystem block address, rather than
a disk address. This is wrong because the range passed in is a
linear representation, while the filesystem block address notation
is a sparse representation. Hence we cannot convert the range direct
to filesystem block units and then use that for calculating the
range to trim.
While this sounds dangerous, the problem is limited to calculating
what AGs need to be trimmed. The code that calcuates the actual
ranges to trim gets the right result (i.e. only ever discards free
space), even though it uses the wrong ranges to limit what is
trimmed. Hence this is not a bug that endangers user data.
Fix this by treating the range as a disk address range and use the
appropriate functions to convert the range into the desired formats
for calculations.
Further, fix the first free extent lookup (the longest) to actually
find the largest free extent. Currently this lookup uses a <=
lookup, which results in finding the extent to the left of the
largest because we can never get an exact match on the largest
extent. This is due to the fact that while we know it's size, we
don't know it's location and so the exact match fails and we move
one record to the left to get the next largest extent. Instead, use
a >= search so that the lookup returns the largest extent regardless
of the fact we don't get an exact match on it.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>
We currently have significant issues with the amount of stack that
allocation in XFS uses, especially in the writeback path. We can
easily consume 4k of stack between mapping the page, manipulating
the bmap btree and allocating blocks from the free list. Not to
mention btree block readahead and other functionality that issues IO
in the allocation path.
As a result, we can no longer fit allocation in the writeback path
in the stack space provided on x86_64. To alleviate this problem,
introduce an allocation workqueue and move all allocations to a
seperate context. This can be easily added as an interposing layer
into xfs_alloc_vextent(), which takes a single argument structure
and does not return until the allocation is complete or has failed.
To do this, add a work structure and a completion to the allocation
args structure. This allows xfs_alloc_vextent to queue the args onto
the workqueue and wait for it to be completed by the worker. This
can be done completely transparently to the caller.
The worker function needs to ensure that it sets and clears the
PF_TRANS flag appropriately as it is being run in an active
transaction context. Work can also be queued in a memory reclaim
context, so a rescuer is needed for the workqueue.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>
Remove the definitions and usage of the macros XFS_BUF_ERROR,
XFS_BUF_GETERROR and XFS_BUF_ISERROR.
Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Remove two variables that serve no purpose in
xfs_alloc_ag_vextent_exact().
Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
Micro-optimize various comparisms by always byteswapping the constant
instead of the variable, which allows to do the swap at compile instead
of runtime.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Blocks for the allocation btree are allocated from and released to
the AGFL, and thus frequently reused. Even worse we do not have an
easy way to avoid using an AGFL block when it is discarded due to
the simple FILO list of free blocks, and thus can frequently stall
on blocks that are currently undergoing a discard.
Add a flag to the busy extent tracking structure to skip the discard
for allocation btree blocks. In normal operation these blocks are
reused frequently enough that there is no need to discard them
anyway, but if they spill over to the allocation btree as part of a
balance we "leak" blocks that we would otherwise discard. We could
fix this by adding another flag and keeping these block in the
rbtree even after they aren't busy any more so that we could discard
them when they migrate out of the AGFL. Given that this would cause
significant overhead I don't think it's worthwile for now.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Now that we have reliably tracking of deleted extents in a
transaction we can easily implement "online" discard support
which calls blkdev_issue_discard once a transaction commits.
The actual discard is a two stage operation as we first have
to mark the busy extent as not available for reuse before we
can start the actual discard. Note that we don't bother
supporting discard for the non-delaylog mode.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
When allocating an extent that is long enough to consume the
remaining free space in an AG, we need to ensure that the allocation
leaves enough space in the AG for any subsequent bmap btree blocks
that are needed to track the new extent. These have to be allocated
in the same AG as we only reserve enough blocks in an allocation
transaction for modification of the freespace trees in a single AG.
xfs_alloc_fix_minleft() has been considering blocks on the AGFL as
free blocks available for extent and bmbt block allocation, which is
not correct - blocks on the AGFL are there exclusively for the use
of the free space btrees. As a result, when minleft is less than the
number of blocks on the AGFL, xfs_alloc_fix_minleft() does not trim
the given extent to leave minleft blocks available for bmbt
allocation, and hence we can fail allocation during bmbt record
insertion.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Instead of finding the per-ag and then taking and releasing the pagb_lock
for every single busy extent completed sort the list of busy extents and
only switch betweens AGs where nessecary. This becomes especially important
with the online discard support which will hit this lock more often.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Update the extent tree in case we have to reuse a busy extent, so that it
always is kept uptodate. This is done by replacing the busy list searches
with a new xfs_alloc_busy_reuse helper, which updates the busy extent tree
in case of a reuse. This allows us to allow reusing metadata extents
unconditionally, and thus avoid log forces especially for allocation btree
blocks.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Every time we reallocate a busy extent, we cause a synchronous log force
to occur to ensure the freeing transaction is on disk before we continue
and use the newly allocated extent. This is extremely sub-optimal as we
have to mark every transaction with blocks that get reused as synchronous.
Instead of searching the busy extent list after deciding on the extent to
allocate, check each candidate extent during the allocation decisions as
to whether they are in the busy list. If they are in the busy list, we
trim the busy range out of the extent we have found and determine if that
trimmed range is still OK for allocation. In many cases, this check can
be incorporated into the allocation extent alignment code which already
does trimming of the found extent before determining if it is a valid
candidate for allocation.
Based on earlier patches from Dave Chinner.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
While we need to make sure we do not reuse busy extents, there is no need
to force out busy extents when moving them between the AGFL and the
freespace btree as we still take care of that when doing the real allocation.
To avoid the log force when just moving extents from the different free
space tracking structures, move the busy search out of
xfs_alloc_get_freelist into the callers that need it, and move the busy
list insert from xfs_free_ag_extent which is used both by AGFL refills
and real allocation to xfs_free_extent, which is only used by the latter.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
A fuzzed filesystem crashed a kernel when freeing an extent with a
block number beyond the end of the filesystem. Convert all the debug
asserts in xfs_free_extent() to active checks so that we catch bad
extents and return that the filesytsem is corrupted rather than
crashing.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Updating the AGF and transactions counters is duplicated between allocating
and freeing extents. Factor the code into a common helper.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
Pass a xfs_alloc_arg structure to xfs_alloc_compute_aligned and derive
the alignment and minlen paramters from it. This cleans up the existing
callers, and we'll need even more information from the xfs_alloc_arg
in subsequent patches. Based on a patch from Dave Chinner.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
Allow manual discards from userspace using the FITRIM ioctl. This is not
intended to be run during normal workloads, as the freepsace btree walks
can cause large performance degradation.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
Add a new xfs_alloc_find_best_extent that does a forward/backward
search in the allocation btree. That code previously was existed
two times in xfs_alloc_ag_vextent_near, once for each search
direction.
Based on an earlier patch from Dave Chinner.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Use a goto label to consolidate all block not found cases, and add a
tracepoint for them. Also clean up a few whitespace issues.
Based on an earlier patch from Dave Chinner.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Ionut Gabriel Popescu <poyo_vl@yahoo.com> submitted a simple change
to eliminate some "may be used uninitialized" warnings when building
XFS. The reported condition seems to be something that GCC did not
used to recognize or report. The warnings were produced by:
gcc version 4.5.0 20100604
[gcc-4_5-branch revision 160292] (SUSE Linux)
Signed-off-by: Ionut Gabriel Popescu <poyo_vl@yahoo.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
[hch: dropped a few hunks that need structural changes instead]
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Dmapi support was never merged upstream, but we still have a lot of hooks
bloating XFS for it, all over the fast pathes of the filesystem.
This patch drops over 700 lines of dmapi overhead. If we'll ever get HSM
support in mainline at least the namespace events can be done much saner
in the VFS instead of the individual filesystem, so it's not like this
is much help for future work.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
When we free a metadata extent, we record it in the per-AG busy
extent array so that it is not re-used before the freeing
transaction hits the disk. This array is fixed size, so when it
overflows we make further allocation transactions synchronous
because we cannot track more freed extents until those transactions
hit the disk and are completed. Under heavy mixed allocation and
freeing workloads with large log buffers, we can overflow this array
quite easily.
Further, the array is sparsely populated, which means that inserts
need to search for a free slot, and array searches often have to
search many more slots that are actually used to check all the
busy extents. Quite inefficient, really.
To enable this aspect of extent freeing to scale better, we need
a structure that can grow dynamically. While in other areas of
XFS we have used radix trees, the extents being freed are at random
locations on disk so are better suited to being indexed by an rbtree.
So, use a per-AG rbtree indexed by block number to track busy
extents. This incures a memory allocation when marking an extent
busy, but should not occur too often in low memory situations. This
should scale to an arbitrary number of extents so should not be a
limitation for features such as in-memory aggregation of
transactions.
However, there are still situations where we can't avoid allocating
busy extents (such as allocation from the AGFL). To minimise the
overhead of such occurences, we need to avoid doing a synchronous
log force while holding the AGF locked to ensure that the previous
transactions are safely on disk before we use the extent. We can do
this by marking the transaction doing the allocation as synchronous
rather issuing a log force.
Because of the locking involved and the ordering of transactions,
the synchronous transaction provides the same guarantees as a
synchronous log force because it ensures that all the prior
transactions are already on disk when the synchronous transaction
hits the disk. i.e. it preserves the free->allocate order of the
extent correctly in recovery.
By doing this, we avoid holding the AGF locked while log writes are
in progress, hence reducing the length of time the lock is held and
therefore we increase the rate at which we can allocate and free
from the allocation group, thereby increasing overall throughput.
The only problem with this approach is that when a metadata buffer is
marked stale (e.g. a directory block is removed), then buffer remains
pinned and locked until the log goes to disk. The issue here is that
if that stale buffer is reallocated in a subsequent transaction, the
attempt to lock that buffer in the transaction will hang waiting
the log to go to disk to unlock and unpin the buffer. Hence if
someone tries to lock a pinned, stale, locked buffer we need to
push on the log to get it unlocked ASAP. Effectively we are trading
off a guaranteed log force for a much less common trigger for log
force to occur.
Ideally we should not reallocate busy extents. That is a much more
complex fix to the problem as it involves direct intervention in the
allocation btree searches in many places. This is left to a future
set of modifications.
Finally, now that we track busy extents in allocated memory, we
don't need the descriptors in the transaction structure to point to
them. We can replace the complex busy chunk infrastructure with a
simple linked list of busy extents. This allows us to remove a large
chunk of code, making the overall change a net reduction in code
size.
Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Remove the XFS_LOG_FORCE argument which was always set, and the
XFS_LOG_URGE define, which was never used.
Split xfs_log_force into a two helpers - xfs_log_force which forces
the whole log, and xfs_log_force_lsn which forces up to the
specified LSN. The underlying implementations already were entirely
separate, as were the users.
Also re-indent the new _xfs_log_force/_xfs_log_force which
previously had a weird coding style.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Currently we define aliases for the buffer flags in various
namespaces, which only adds confusion. Remove all but the XBF_
flags to clean this up a bit.
Note that we still abuse XFS_B_ASYNC/XBF_ASYNC for some non-buffer
uses, but I'll clean that up later.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
Now that the perag structure is allocated memory rather than held in
an array, we don't need to have the busy extent array external to
the structure. Embed it into the perag structure to avoid needing an
extra allocation when setting up.
Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Jan Kara