A recent bug report uncovered a scenario where a filesystem never
runs with freespace_initialized, and therefore the user observes
significantly degraded write performance by virtue of running the
early bucket allocator. The associated bug aside, the primary cause
of the performance drop in this particular instance is that the
early bucket allocator does not update the allocation cursor. This
means that every allocation walks the alloc btree from the first
bucket of the associated device looking for a bucket marked as free
space.
Update the early allocator code to set the alloc cursor to the last
processed position in the tree, similar to how the freelist
allocator behaves. With the alloc_cursor being updated, the retry
logic also needs to be updated to restart from the beginning of the
device when a free bucket is not available between the cursor and
the end of the device. Track the restart position in a first_bucket
variable to make the code a bit more easily readable and consistent
with the freelist allocator.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
bcachefs had a transient bug where freespace_initialized was not
properly being set, which lead to unexpected use of the early bucket
allocator at runtime. This issue has been fixed, but the existence
of it uncovered a coherency issue in the early bucket allocation
code that is somewhat related to how uncached iterators deal with
the key cache.
The problem itself manifests as occasional failure of generic/113
due to corruption, often seen as a duplicate backpointer or multiple
data types per-bucket error. The immediate cause of the error is a
racing bucket allocation along the lines of the following sequence:
- Task 1 selects key A in bch2_bucket_alloc_early() and schedules.
- Task 2 selects the same key A, but proceeds to complete the
allocation and associated I/O, after which it releases the
open_bucket.
- Task 1 resumes with key A, but does not recognize the bucket is
now allocated because the open_bucket has been removed
from the hash when it was released in the previous step.
This generally shouldn't happen because the allocating task updates
the alloc btree key before releasing the bucket. This is not
sufficient in this particular instance, however, because an uncached
iterator for a cached btree doesn't actually lock the key cache slot
when no key exists for a given slot in the cache. Thus the fact that
the allocation side updates the cached key means that multiple
uncached iters can stumble across the same alloc key and duplicate
the bucket allocation as described above.
This is something that probably needs a longer term fix in the
iterator code. As a short term fix, close the race through explicit
use of a cached iterator for likely allocation candidates. We don't
want to scan the btree with a cached iterator because that would
unnecessarily pollute the cache. This mitigates cache pollution by
primarily scanning the tree with an uncached iterator, but closes
the race by creating a key cache entry for any prospective slot
prior to the bucket allocation attempt (also similar to how
_alloc_freelist() works via try_alloc_bucket()). This survives many
iterations of generic/113 on a kernel hacked to always use the early
bucket allocator.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
We're using more stack than we'd like in a number of functions, and
btree_trans is the biggest object that we stack allocate.
But we have to do a heap allocatation to initialize it anyways, so
there's no real downside to heap allocating the entire thing.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
More reorganization, this splits up io.c into
- io_read.c
- io_misc.c - fallocate, fpunch, truncate
- io_write.c
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Now we also print the open_buckets owned by each write_point - this is
to help with debugging a shutdown hang.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
clang had a few more warnings about enum conversion, and also didn't
like the opts.c initializer.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
We were freeing open buckets on the writepoint list, but forgetting to
take them off the writepoint list - whoops
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Recovery and fsck have many different passes/jobs to do, which always
run in the same order - but not all of them run all the time. Some are
for fsck, some for unclean shutdown, some for version upgrades.
This adds some new structure: a defined list of recovery passes that we
can run in a loop, as well as consolidating the log messages.
The main benefit is consolidating the "should run this recovery pass"
logic, as well as cleaning up the "this recovery pass has finished"
state; instead of having a bunch of ad-hoc state bits in c->flags, we've
now got c->curr_recovery_pass.
By consolidating the "should run this recovery pass" logic, in the
future on disk format upgrades will be able to say "upgrading to this
version requires x passes to run", instead of forcing all of fsck to
run.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Add another watermark for journal reclaim - this is needed for the next
patches, that unify BCH_WATERMARK with JOURNAL_WATERMARK.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
- We may need to drop btree locks before taking the writepoint_lock, as
is done in other places.
- We should be using open_bucket_free_unused(), so that we don't waste
space.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
On Mon, 29 May 2023, Mikulas Patocka wrote:
> The oops happens in set_btree_iter_dontneed and it is caused by the fact
> that iter->path is NULL. The code in try_alloc_bucket is buggy because it
> sets "struct btree_iter iter = { NULL };" and then jumps to the "err"
> label that tries to dereference values in "iter".
Here I'm sending a patch for it.
From: Mikulas Patocka <mpatocka@redhat.com>
The function try_alloc_bucket sets the variable "iter" to NULL and then
(on various error conditions) jumps to the label "err". On the "err"
label, it calls "set_btree_iter_dontneed" that tries to dereference
"iter->trans" and "iter->path".
So, we get an oops on error condition.
This patch fixes the crash by testing that iter.trans and iter.path is
non-zero before calling set_btree_iter_dontneed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
We have one caller that cycles the rcu lock solely for this call
(via target_rw_devs()), and we'd like to add another. Simplify
things by pushing the rcu lock down into bch2_target_to_mask(),
similar to how bch2_dev_in_target() works.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Introduce new helpers for a common pattern:
bch2_trans_iter_init();
bch2_btree_iter_peek_slot();
- bch2_bkey_get_iter_type() returns -ENOENT if it doesn't find a key of
the correct type
- bch2_bkey_get_val_typed() copies the val out of the btree to a
(typically stack allocated) variable; it handles the case where the
value in the btree is smaller than the current version of the type,
zeroing out the remainder.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
We don't store backpointers in alloc keys anymore, since we gained the
btree write buffer.
This patch drops support for backpointers in alloc keys, and revs the on
disk format version so that we know a fsck is required.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This implements a new shutdown path for erasure coding, which is needed
for the upcoming BCH_WRITE_WAIT_FOR_EC write path.
The process is:
- Cancel new stripes being built up
- Close out/cancel open buckets on write points or the partial list
that are for stripes
- Shutdown rebalance/copygc
- Then wait for in flight new stripes to finish
With BCH_WRITE_WAIT_FOR_EC, move ops will be waiting on stripes to fill
up before they complete; the new ec shutdown path is needed for shutting
down copygc/rebalance without deadlocking.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This will be used for move writes, which will be waiting until the
stripe is created to do the index update. They need to prevent the
stripe from being reclaimed until their index update is done, so we need
another refcount that just keeps the stripe open.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
# Conflicts:
# fs/bcachefs/ec.c
# fs/bcachefs/io.c
Now, any open_bucket can go on the partial list: allocating from the
partial list has been moved to its own dedicated function,
open_bucket_add_bucets() -> bucket_alloc_set_partial().
In particular, this means that erasure coded buckets can safely go on
the partial list; the new location works with the "allocate an ec bucket
first, then the rest" logic.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This adds a new helper, bch2_trans_mutex_lock(), for locking a mutex -
dropping and retaking btree locks as needed.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This code predates plumbing btree_trans through the bucket allocation
path: switching to it fixes a deadlock due to using multiple btree_trans
at the same time, which we never want to do.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This improves the nocow lock table so that hash table entries have
multiple locks, and locks specify which bucket they're for - i.e. we can
now resolve hash collisions.
This is important because the allocator has to skip buckets that are
locked in the nocow lock table, and previously hash collisions would
cause it to spuriously skip unlocked buckets.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This adds support for nocow mode, where we do writes in-place when
possible. Patch components:
- New boolean filesystem and inode option, nocow: note that when nocow
is enabled, data checksumming and compression are implicitly disabled
- To prevent in-place writes from racing with data moves
(data_update.c) or bucket reuse (i.e. a bucket being reused and
re-allocated while a nocow write is in flight, we have a new locking
mechanism.
Buckets can be locked for either data update or data move, using a
fixed size hash table of two_state_shared locks. We don't have any
chaining, meaning updates and moves to different buckets that hash to
the same lock will wait unnecessarily - we'll want to watch for this
becoming an issue.
- The allocator path also needs to check for in-place writes in flight
to a given bucket before giving it out: thus we add another counter
to bucket_alloc_state so we can track this.
- Fsync now may need to issue cache flushes to block devices instead of
flushing the journal. We add a device bitmask to bch_inode_info,
ei_devs_need_flush, which tracks devices that need to have flushes
issued - note that this will lead to unnecessary flushes when other
codepaths have already issued flushes, we may want to replace this with
a sequence number.
- New nocow write path: look up extents, and if they're writable write
to them - otherwise fall back to the normal COW write path.
XXX: switch to sequence numbers instead of bitmask for devs needing
journal flush
XXX: ei_quota_lock being a mutex means bch2_nocow_write_done() needs to
run in process context - see if we can improve this
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
The btree key cache mainly helps with lock contention, at the cost of
additional memory overhead. During some fsck passes the memory overhead
really matters, but fsck is single threaded so lock contention is an
issue - so skipping the key cache during fsck will help with
performance.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This patch adds backpointers: we now have a reverse index from device
and offset on that device (specifically, offset within a bucket) back to
btree nodes and (non cached) data extents.
The first 40 backpointers within a bucket are stored in the alloc key;
after that backpointers spill over to the next backpointers btree. This
is to help avoid performance regressions from additional btree updates
on large streaming workloads.
This patch adds all the code for creating, checking and repairing
backpointers. The next patch in the series is going to use backpointers
for copygc - finally getting rid of the need to scan all extents to do
copygc.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
It's possible to do btree updates before going RW by adding them to the
list of updates for journal replay to do, but this is limited by what
fits in RAM. This patch switches the second alloc info phase to run
after going RW - btree_gc has already ensured the alloc btree itself is
correct - and tweaks the allocation path to deal with the potential
small inconsistencies.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Provide inline versions of some allocation functions
- bch2_alloc_sectors_done_inlined()
- bch2_alloc_sectors_append_ptrs_inlined()
and use them in the core IO path.
Also, inline bch2_extent_update_i_size_sectors() and
bch2_bkey_append_ptr().
In the core write path, function call overhead matters - every function
call is a jump to a new location and a potential cache miss.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This separates out the slowpath into a separate function, and inlines
bch2_alloc_v4_mut into bch2_trans_start_alloc_update(), the main place
it's called.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This patch introduces
- bpos_eq()
- bpos_lt()
- bpos_le()
- bpos_gt()
- bpos_ge()
and equivalent replacements for bkey_cmp().
Looking at the generated assembly these could probably be improved
further, but we already see a significant code size improvement with
this patch.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
checkpatch.pl gives lots of warnings that we don't want - suggested
ignore list:
ASSIGN_IN_IF
UNSPECIFIED_INT - bcachefs coding style prefers single token type names
NEW_TYPEDEFS - typedefs are occasionally good
FUNCTION_ARGUMENTS - we prefer to look at functions in .c files
(hopefully with docbook documentation), not .h
file prototypes
MULTISTATEMENT_MACRO_USE_DO_WHILE
- we have _many_ x-macros and other macros where
we can't do this
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
- add bch2_dev_usage_read_fast(), which doesn't return by value -
bch_dev_usage is big enough that we don't want the silent memcpy
- tweak the allocation path to only call bch2_dev_usage_read() once per
bucket allocated
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
We don't want to fire the bucket_alloc_fail tracepoint on transaction
restart, when we can retry immediately - only when we the allocation
actually has to block.
Also, switch from sched_clock() to local_clock(), as we've been doing
elsewhere.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
We were incorrectly returning -BCH_ERR_insufficient_devices when we'd
received a different error from bch2_bucket_alloc_trans(), which
(erronously) turns into -EROFS further up the call chain.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This refactoring puts our various allocation path counters into a
dedicated struct - the upcoming nocow patch is going to add another
counter.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
It now includes more info - whether the bucket was for metadata or data
- and also call it in the same place as the bucket_alloc_fail
tracepoint.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Continuing the saga of introducing private dedicated error codes for
each error path, this patch converts ENOSPC to error codes that are
subtypes of ENOSPC. We've recently had a test failure where we got
-ENOSPC where we shouldn't have, and didn't have enough information to
tell where it came from, so this patch will solve that problem.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Also, do some reorganizing/renaming, convert atomic counters in bch_fs
to persistent counters, and add a few missing counters.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Nested btree transactions require special care, and an upcoming patch is
going to add assertions to that effect. We don't want to be using them
unnecessarily, so this patch switches bch2_bucket_trans_early() to not
handle transaction restarts.
This patch also adds a cursor so that on transaction restart we can
continue scanning from where the previous search for an empty bucket
left off.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Now that we have error codes, with subtypes, we can switch to our own
error code for transaction restarts - and even better, a distinct error
code for each transaction restart reason: clearer code and better
debugging.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
In bch2_bucket_alloc_trans(), we're iterating over buckets - but not
directly with an iterator, since we're iterating over the freespace
btree.
This means that we need to clear iter->path->preserve, otherwise we'll
end up retaining a btree_path for every alloc key we touched - which is
not what we want here.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Instead of overloading standard error codes (EINTR/EAGAIN), and defining
short lists of error codes in multiple places that potentially end up
overlapping & conflicting, we're now going to have one master list of
error codes.
Error codes are defined with an x-macro: thus we also have
bch2_err_str() now.
Also, error codes have a class field. Now, instead of checking for
errors with ==, code should use bch2_err_matches(), which returns true
if the error is equal to or a sub-error of the error class.
This means we can define unique errors for every source location where
an error is generated, which will help improve our error messages.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
