We shouldn't be doing the unlock/relock dance when we're not using a
path - this fixes an assertion pop when called from btree node scan.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Consolidate bch2_gc_check_topology() and btree_node_interior_verify(),
and replace them with an improved version,
bch2_btree_node_check_topology().

This checks that children of an interior node correctly span the full
range of the parent node with no overlaps.

Also, ensure that topology repairs at runtime are always a fatal error;
in particular, this adds a check in btree_iter_down() - if we don't find
a key while walking down the btree that's indicative of a topology error
and should be flagged as such, not a null ptr deref.

Some checks in btree_update_interior.c remaining BUG_ONS(), because we
already checked the node for topology errors when starting the update,
and the assertions indicate that we _just_ corrupted the btree node -
i.e. the problem can't be that existing on disk corruption, they
indicate an actual algorithmic bug.

In the future, we'll be annotating the fsck errors list with which
recovery pass corrects them; the open coded "run explicit recovery pass
or fatal error" in bch2_btree_node_check_topology() will in the future
be done for every fsck_err() call.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Various phases of fsck involve checking references from one btree to
another: this means doing a sequential scan of one btree, and then
mostly random access into the second.

This is particularly painful for checking extents <-> backpointers; we
can prefetch btree node access on the sequential scan, but not on the
random access portion, and this is particularly painful on spinning
rust, where we'd like to keep the pipeline fairly full of btree node
reads so that the elevator can reduce seeking.

This patch implements prefetching and pinning of the portion of the
btree that we'll be doing random access to. We already calculate how
much of the random access btree will fit in memory so it's a fairly
straightforward change.

This will put more pressure on system memory usage, so we introduce a
new option, fsck_memory_usage_percent, which is the percentage of total
system ram that fsck is allowed to pin.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

This converts -EIOs related to btree node errors to private error codes,
which will help with some ongoing debugging by giving us better error
messages.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

btree_and_journal_iter is old code that we want to get rid of, but we're
not ready to yet.

lack of btree node prefetching is, it turns out, a real performance
issue for fsck on spinning rust, so - add it.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs btree nodes are big - typically 256k - and btree roots are
pinned in memory. As we're now up to 18 btrees, we now have significant
memory overhead in mostly empty btree roots.

And in the future we're going to start enforcing that certain btree node
boundaries exist, to solve lock contention issues - analagous to XFS's
AGIs.

Thus, we need to start allocating smaller btree node buffers when we
can. This patch changes code that refers to the filesystem constant
c->opts.btree_node_size to refer to the btree node buffer size -
btree_buf_bytes() - where appropriate.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>