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"bcachefs; Fix deadlock in bch2_btree_update_start()" was a significant
performance regression (nearly 50%) on multithreaded random writes with
fio.
The reason is that the journal watermark checks multiple things,
including the state of the btree write buffer, and on multithreaded
update heavy workloads we're bottleneked on write buffer flushing - we
don't want kicknig off btree updates to depend on the state of the write
buffer.
This isn't strictly correct; the interior btree update path does do
write buffer updates, but it's a tiny fraction of total accounting
updates and we're more concerned with space in the journal itself.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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prep work for lifting out of fs/bcachefs/
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Recently a severe performance regression was discovered, which bisected
to
a6548c8b5eb5 bcachefs: Avoid flushing the journal in the discard path
It turns out the old behaviour, which issued excessive journal flushes,
worked around a performance issue where queueing delays would cause the
journal to not be able to write quickly enough and stall.
The journal flushes masked the issue because they periodically flushed
the device write cache, reducing write latency for non flushes.
This patch reworks the journalling code to allow more than one
(non-flush) write to be in flight at a time. With this patch, doing 4k
random writes and an iodepth of 128, we are now able to hit 560k iops to
a Samsung 970 EVO Plus - previously, we were stuck in the ~200k range.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Prep work for having multiple journal writes in flight.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Prep work for having multiple journal writes in flight.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Previously, any time we failed to get a journal reservation we'd retry,
with the journal lock held; but this isn't necessary given
wait_event()/wake_up() ordering.
This avoids performance cliffs when the journal starts to get backed up
and lock contention shoots up.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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We don't want journal write completions to be blocked behind btree
transactions - io_complete_wq is used for btree updates after data and
metadata writes.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Previosuly, the transaction commit path would have to add keys to the
btree write buffer as a separate operation, requiring additional global
synchronization.
This patch introduces a new journal entry type, which indicates that the
keys need to be copied into the btree write buffer prior to being
written out. We switch the journal entry type back to
JSET_ENTRY_btree_keys prior to write, so this is not an on disk format
change.
Flushing the btree write buffer may require pulling keys out of journal
entries yet to be written, and quiescing outstanding journal
reservations; we previously added journal->buf_lock for synchronization
with the journal write path.
We also can't put strict bounds on the number of keys in the journal
destined for the write buffer, which means we might overflow the size of
the preallocated buffer and have to reallocate - this introduces a
potentially fatal memory allocation failure. This is something we'll
have to watch for, if it becomes an issue in practice we can do
additional mitigation.
The transaction commit path no longer has to explicitly check if the
write buffer is full and wait on flushing; this is another performance
optimization. Instead, when the btree write buffer is close to full we
change the journal watermark, so that only reservations for journal
reclaim are allowed.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Add a new lock for synchronizing between journal IO path and btree write
buffer flush.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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This introduces a new helper for connecting time_stats to state changes,
i.e. when taking journal reservations is blocked for some reason.
We use this to track separately the different reasons the journal might
be blocked - i.e. space in the journal full, or the journal pin fifo
full.
Also do some cleanup and improvements on the time stats code.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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This deletes the complicated and somewhat expensive journal
pre-reservation machinery in favor of just using journal watermarks:
when the journal is more than half full, we run journal reclaim more
aggressively, and when the journal is more than 3/4s full we only allow
journal reclaim to get new journal reservations.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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This unifies JOURNAL_WATERMARK with BCH_WATERMARK; we're working towards
specifying watermarks once in the transaction commit path.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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This patch
- Adds a mechanism for queuing up journal entries prior to the journal
being started, which will be used for early journal log messages
- Adds bch2_fs_log_msg() and improves bch2_trans_log_msg(), which now
take format strings. bch2_fs_log_msg() can be used before or after
the journal has been started, and will use the appropriate mechanism.
- Deletes the now obsolete bch2_journal_log_msg()
- And adds more log messages to the recovery path - messages for
journal/filesystem started, journal entries being blacklisted, and
journal replay starting/finishing.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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On startup, we need to ensure the first journal entry written is a flush
write: after a clean shutdown we generally don't read the journal, which
means we might be overwriting whatever was there previously, and there
must always be at least one flush entry in the journal or recovery will
fail.
Found by fstests generic/388.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Since journal reclaim -> btree key cache flushing may require the
allocation of new btree nodes, it has an implicit dependency on copygc
in order to make forward progress - so we should avoid blocking copygc
unless the journal is really close to full.
This introduces watermarks to replace our single MAY_GET_UNRESERVED bit
in the journal, and adds a watermark for copygc and plumbs it through.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Less system noise.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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Previous patch just moved responsibility for incrementing the journal
sequence number and initializing the new journal entry from
__journal_entry_close() to journal_entry_open(); this patch makes the
analagous change for journal reservation state, incrementing the index
into array of journal_bufs at open time.
This means that __journal_entry_close() never fails to close an open
journal entry, which is important for the next patch that will change
our emergency shutdown behaviour.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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It makes the code more readable if we work off of sequence numbers,
instead of direct indexes into the array of journal buffers.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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This replaces the journal flag JOURNAL_NEED_WRITE with per-journal buf
state - more explicit, and solving a race in the old code that would
lead to entries being opened and written unnecessarily.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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This cacheline aligns struct journal, and puts j->reservations and
j->prereserved on their own cacheline - we may want to split them up in
a separate patch.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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This patch was originally to work around the journal geting stuck in
nochanges mode - but that was just a hack, we needed to fix the actual
bug. It should be fixed now, so revert it.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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With BTREE_ITER_WITH_JOURNAL, there's no longer any restrictions on the
order we have to replay keys from the journal in, and we can also start
up journal reclaim right away - and delete a bunch of code.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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This adds more latency/event measurements and breaks some apart into
more events. Journal writes are broken apart into flush writes and
noflush writes, btree compactions are broken out from btree splits,
btree mergers are added, as well as btree_interior_updates - foreground
and total.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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This converts journal_write_delay, journal_flush_disabled, and
journal_reclaim_delay to normal filesystems options, and also adds them
to the superblock.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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This was used for recording which inodes have been modified by in flight
journal writes, but was broken and has been superceded.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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This tweaks the journal code to always act as if there's space available
in nochanges mode, when we're not going to be doing any writes. This
helps in recovering filesystems that won't mount because they need
journal replay and the journal has gotten stuck.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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Journal write errors were racing with the submission path - potentially
causing writes to other replicas to not get submitted.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
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jset->last_seq is in the region that's encrypted - on journal write
completion, we were using it and getting garbage. This patch shadows it
to fix.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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If the journal reclaim thread makes it to the timeout without ever
initializing j->last_flushed, we could end up sleeping for a very long
time.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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We need to flush the btree key cache when it's too dirty, because
otherwise the shrinker won't be able to reclaim memory - this is done by
journal reclaim. But journal reclaim also kicks btree node writes: this
meant that btree node writes were getting kicked much too often just
because we needed to flush btree key cache keys.
This patch splits journal pins into two different lists, and teaches
journal reclaim to not flush btree node writes when it only needs to
flush key cache keys.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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JOURNAL_RES_GET_RESERVED should only be used for updatse that need to be
done to free up space in the journal. In particular, when we're flushing
keys from the key cache, if we're flushing them out of order we
shouldn't be using it, since we're using up our remaining space in the
journal without dropping a pin that will let us make forward progress.
With this patch, BTREE_INSERT_JOURNAL_RECLAIM without
BTREE_INSERT_JOURNAL_RESERVED may return -EAGAIN - we can't wait on
journal reclaim if we're already in journal reclaim.
This means we need to propagate these errors up to journal reclaim,
indicating that flushing a journal pin should be retried in the future.
This is prep work for a patch to change the way journal reclaim works,
to split out flushing key cache keys because the btree key cache is too
dirty from journal reclaim because we need space in the journal.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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All writes prior to a journal write need to be flushed before the
journal write itself happens. On single device filesystems, it suffices
to mark the write with REQ_PREFLUSH|REQ_FUA, but on multi device
filesystems we need to issue flushes to every device - and wait for them
to complete - before issuing the journal writes. Previously, we were
issuing flushes to every device, but we weren't waiting for them to
complete before issuing the journal writes.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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With various newer key types - stripe keys, inline data extents - the
old approach of calculating the maximum size of the value is becoming
more and more error prone. Better to switch to bkey_on_stack, which can
dynamically allocate if necessary to handle any size bkey.
In particular we also want to get rid of BKEY_EXTENT_VAL_U64s_MAX.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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- Try to always keep 1/8th of the journal free, on top of
pre-reservations
- Move the check for whether the journal is stuck to
bch2_journal_space_available, and make it only fire when there aren't
any journal writes in flight (that might free up space by updating
last_seq)
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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This patch adds a flag to journal entries which, if set, indicates that
they weren't done as flush/fua writes.
- non flush/fua journal writes don't update last_seq (i.e. they don't
free up space in the journal), thus the journal free space
calculations now check whether nonflush journal writes are currently
allowed (i.e. are we low on free space, or would doing a flush write
free up a lot of space in the journal)
- write_delay_ms, the user configurable option for when open journal
entries are automatically written, is now interpreted as the max
delay between flush journal writes (default 1 second).
- bch2_journal_flush_seq_async is changed to ensure a flush write >=
the requested sequence number has happened
- journal read/replay must now ignore, and blacklist, any journal
entries newer than the most recent flush entry in the journal. Also,
the way the read_entire_journal option is handled has been improved;
struct journal_replay now has an entry, 'ignore', for entries that
were read but should not be used.
- assorted refactoring and improvements related to journal read in
journal_io.c and recovery.c
Previously, we'd have to issue a flush/fua write every time we
accumulated a full journal entry - typically the bucket size. Now we
need to issue them much less frequently: when an fsync is requested, or
it's been more than write_delay_ms since the last flush, or when we need
to free up space in the journal. This is a significant performance
improvement on many write heavy workloads.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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This patch increases the maximum journal buffers in flight from 2 to 4 -
this will be particularly helpful when in the future we stop requiring
flush+fua for every journal write.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Various filesystem usage counters are kept in percpu counters, with one
set per in flight journal buffer. Right now all the code that deals with
it assumes that there's only two buffers/sets of counters, but the
number of journal bufs is getting increased to 4 in the next patch - so
refactor that code to not assume a constant.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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This is to make tracing easier.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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We were incorrectly detecting a journal deadlock - the journal filling
up - when only the journal pin fifo had filled up; if the journal pin
fifo is full that just means we need to wait on reclaim.
This plumbs through better error reporting so we can better discriminate
in the journal_res_get path what's going on.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Improved the way we track various state by adding j->err_seq, which
records the first journal sequence number that encountered an error
being written, and j->last_empty_seq, which records the most recent
journal entry that was completely empty.
Also, use the low bits of the journal sequence number to index the
corresponding journal_buf.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Now, we store blacklisted journal sequence numbers in the superblock,
not the journal: this helps to greatly simplify the code, and more
importantly it's now implemented in a way that doesn't require all btree
nodes to be visited before starting the journal - instead, we
unconditionally blacklist the next 4 journal sequence numbers after an
unclean shutdown.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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