For each bucket we track when the bucket became nonempty and when it
became empty again: if we can ensure that there will be no journal
flushes in the range [nonempty, empty) (possibly because they occured at
the same journal sequence number), then it's safe to reuse the bucket
without waiting for a journal commit.
This is a major performance optimization for erasure coding, where
writes are initially replicated, but the extra replicas are quickly
dropped: if those buckets are reused and overwritten without issuing a
cache flush to the underlying device, then they only cost bus bandwidth.
But there's a tricky corner case when there's multiple empty -> nonempty
-> empty transitions in quick succession, i.e. when data is getting
overwritten immediately as it's being written.
If this happens and the previous empty transition hasn't been flushed,
we need to continue tracking the previous nonempty transition - not
start a new one.
Fixing this means we now need to track both the nonempty and empty
transitions in bch_alloc_v4.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
The fragmentation_lru field hasn't been needed since we reworked the LRU
btrees to use the btree write buffer; previously it was used to resolve
collisions, but the revised LRU btree uses the backpointer (the bucket)
as part of the key.
It should have been deleted at the time of the LRU rework; since it
wasn't, that left places for bugs to hide, in check/repair.
This fixes LRU fsck on a filesystem image helpfully provided by a user
who disappeared before I could get his name for the reported-by.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
we allow new fields to be added to existing key types, and new versions
should treat them as being zeroed; this was not handled in
alloc_v4_validate.
Reported-by: syzbot+3b2968fa4953885dd66a@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Add a separate counter to bch_alloc_v4 for amount of striped data; this
lets us separately track striped and unstriped data in a bucket, which
lets us see when erasure coding has failed to update extents with stripe
pointers, and also find buckets to continue updating if we crash mid way
through creating a new stripe.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
