Btree nodes are log structured; thus, we need to emit whiteouts when
we're deleting a key that's been written out to disk.
k->needs_whiteout tracks whether a key will need a whiteout when it's
deleted, and this requires some careful handling; e.g. the key we're
deleting may not have been written out to disk, but it may have
overwritten a key that was - thus we need to carry this flag around on
overwrites.
Invariants:
There may be multiple key for the same position in a given node (because
of overwrites), but only one of them will be a live (non deleted) key,
and only one key for a given position will have the needs_whiteout flag
set.
Additionally, we don't want to carry around whiteouts that need to be
written in the main searchable part of a btree node - btree_iter_peek()
will have to skip past them, and this can lead to an O(n^2) issues when
doing sequential deletions (e.g. inode rm/truncate). So there's a
separate region in the btree node buffer for unwritten whiteouts; these
are merge sorted with the rest of the keys we're writing in the btree
node write path.
The unwritten whiteouts was a later optimization that bch2_sort_keys()
didn't take into account; the unwritten whiteouts area means that we
never have deleted keys with needs_whiteout set in the main searchable
part of a btree node.
That means we can simplify and optimize some sort paths, and eliminate
an assertion that syzbot found:
- Unless we're in the btree node write path, it's always ok to drop
whiteouts when sorting
- When sorting for a btree node write, we drop the whiteout if it's not
from the unwritten whiteouts area, or if it's overwritten by a real
key at the same position.
This completely eliminates some tricky logic for propagating the
needs_whiteout flag: syzbot was able to hit the assertion that checked
that there shouldn't be more than one key at the same pos with
needs_whiteout set, likely due to a combination of flipping on
needs_whiteout on all written keys (they need whiteouts if overwritten),
combined with not always dropping unneeded whiteouts, and the tricky
logic in the sort path for preserving needs_whiteout that wasn't really
needed.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
It's no longer legal to use a zero size array as a flexible array
member - this causes UBSAN to complain.
This patch switches our zero size arrays to normal flexible array
members when possible, and inserts casts in other places (e.g. where we
use the zero size array as a marker partway through an array).
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
The main function of bch2_sort_repack_merge() was to call .key_normalize
on every key, which drops stale (cached) pointers - it hasn't actually
merged extents in quite some time.
But bch2_gc_gens() now works on individual keys - we used to gc old gens
by rewriting entire btree nodes. With that gone, there's no need for
internal btree code to be calling .key_normalize anymore.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
bcachefs has been aggressively migrating filesystems and btree nodes to
the new format for quite some time - this shouldn't affect anyone
anymore, and lets us delete a _lot_ of code. Also, it frees up
KEY_TYPE_discard for a new whiteout key type for snapshots.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Long overdue cleanup - this converts btree_node_iter_large uses to
sort_iter.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
The whiteout compaction path - as opposed to just dropping whiteouts -
is now only needed for extents, and soon will only be needed for extent
btree nodes in the old format.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
this lets us get rid of a lot of extra switch statements - in a lot of
places we dispatch on the btree node type, and then the key type, so
this is a nice cleanup across a lot of code.
Also improve the on disk format versioning stuff.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
