tag name | bcachefs-2025-03-24 (97777931665a7c417a59d61ed056271bb48a40d3) |
tag date | 2025-03-24 10:37:39 -0400 |
tagged by | Kent Overstreet <kent.overstreet@linux.dev> |
tagged object | commit d8bdc8daac... |
bcachefs updates for 6.15
On disk format is now soft frozen: no more required/automatic are
anticipated before taking off the experimental label.
Major changes/features since 6.14:
- Scrub
- Blocksize greater than page size support
- A number of "rebalance spinning and doing no work" issues have been
fixed; we now check if the write allocation will succeed in
bch2_data_update_init(), before kicking off the read.
There's still more work to do in this area. Later we may want to add
another bitset btree, like rebalance_work, to track "extents that
rebalance was requested to move but couldn't", e.g. due to destination
target having insufficient online devices.
- We can now support scaling well into the petabyte range: latest
bcachefs-tools will pick an appropriate bucket size at format time to
ensure fsck can run in available memory (e.g. a server with 256GB of
ram and 100PB of storage would want 16MB buckets).
On disk format changes:
- 1.21: cached backpointers (scalability improvement)
Cached replicas now get backpointers, which means we no longer rely on
incrementing bucket generation numbers to invalidate cached data: this
lets us get rid of the bucket generation number garbage collection,
which had to periodically rescan all extents to recompute bucket
oldest_gen.
Bucket generation numbers are now only used as a consistency check,
but they're quite useful for that.
- 1.22: stripe backpointers
Stripes now have backpointers: erasure coded stripes have their own
checksums, separate from the checksums for the extents they contain
(and stripe checksums also cover the parity blocks). This is required
for implementing scrub for stripes.
- 1.23: stripe lru (scalability improvement)
Persistent lru for stripes, ordered by "number of empty blocks". This
is used by the stripe creation path, which depending on free space
may create a new stripe out of a partially empty existing stripe
instead of starting a brand new stripe.
This replaces an in-memory heap, and means we no longer have to read
in the stripes btree at startup.
- 1.24: casefolding
Case insensitive directory support, courtesy of Valve.
This is an incompatible feature, to enable mount with
-o version_upgrade=incompatible
- 1.25: extent_flags
Another incompatible feature requiring explicit opt-in to enable.
This adds a flags entry to extents, and a flag bit that marks extents
as poisoned.
A poisoned extent is an extent that was unreadable due to checksum
errors. We can't move such extents without giving them a new checksum,
and we may have to move them (for e.g. copygc or device evacuate).
We also don't want to delete them: in the future we'll have an API
that lets userspace ignore checksum errors and attempt to deal with
simple bitrot itself. Marking them as poisoned lets us continue to
return the correct error to userspace on normal read calls.
Other changes/features:
- BCH_IOCTL_QUERY_COUNTERS: this is used by the new 'bcachefs fs top'
command, which shows a live view of all internal filesystem counters.
- Improved journal pipelining: we can now have 16 journal writes in
flight concurrently, up from 4. We're logging significantly more to
the journal than we used to with all the recent disk accounting
changes and additions, so some users should see a performance
increase on some workloads.
- BCH_MEMBER_STATE_failed: previously, we would do no IO at all to
devices marked as failed. Now we will attempt to read from them, but
only if we have no better options.
- New option, write_error_timeout: devices will be kicked out of the
filesystem if all writes have been failing for x number of seconds.
We now also kick devices out when notified by blk_holder_ops that
they've gone offline.
- Device option handling improvements: the discard option should now be
working as expected (additionally, in -tools, all device options that
can be set at format time can now be set at device add time, i.e.
data_allowed, state).
- We now try harder to read data after a checksum error: we'll do
additional retries if necessary to a device after after it gave us
data with a checksum error.
- More self healing work: the full inode <-> dirent consistency checks
that are currently run by fsck are now also run every time we do a
lookup, meaning we'll be able to correct errors at runtime. Runtime
self healing will be flipped on after the new changes have seen more
testing, currently they're just checking for consistency.
- KMSAN fixes: our KMSAN builds should be nearly clean now, which will
put a massive dent in the syzbot dashboard.
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