bcachefs: Nocow support

This adds support for nocow mode, where we do writes in-place when
possible. Patch components:

 - New boolean filesystem and inode option, nocow: note that when nocow
   is enabled, data checksumming and compression are implicitly disabled

 - To prevent in-place writes from racing with data moves
   (data_update.c) or bucket reuse (i.e. a bucket being reused and
   re-allocated while a nocow write is in flight, we have a new locking
   mechanism.

   Buckets can be locked for either data update or data move, using a
   fixed size hash table of two_state_shared locks. We don't have any
   chaining, meaning updates and moves to different buckets that hash to
   the same lock will wait unnecessarily - we'll want to watch for this
   becoming an issue.

 - The allocator path also needs to check for in-place writes in flight
   to a given bucket before giving it out: thus we add another counter
   to bucket_alloc_state so we can track this.

 - Fsync now may need to issue cache flushes to block devices instead of
   flushing the journal. We add a device bitmask to bch_inode_info,
   ei_devs_need_flush, which tracks devices that need to have flushes
   issued - note that this will lead to unnecessary flushes when other
   codepaths have already issued flushes, we may want to replace this with
   a sequence number.

 - New nocow write path: look up extents, and if they're writable write
   to them - otherwise fall back to the normal COW write path.

XXX: switch to sequence numbers instead of bitmask for devs needing
journal flush

XXX: ei_quota_lock being a mutex means bch2_nocow_write_done() needs to
run in process context - see if we can improve this

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

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/bcachefs/btree_io.c b/fs/bcachefs/btree_io.c
index dfa45cf4021f..87d80a59dd7e 100644
--- a/fs/bcachefs/btree_io.c
+++ b/fs/bcachefs/btree_io.c
@@ -1832,7 +1832,8 @@ static void btree_write_submit(struct work_struct *work)
 	bkey_for_each_ptr(bch2_bkey_ptrs(bkey_i_to_s(&tmp.k)), ptr)
 		ptr->offset += wbio->sector_offset;
 
-	bch2_submit_wbio_replicas(&wbio->wbio, wbio->wbio.c, BCH_DATA_btree, &tmp.k);
+	bch2_submit_wbio_replicas(&wbio->wbio, wbio->wbio.c, BCH_DATA_btree,
+				  &tmp.k, false);
 }
 
 void __bch2_btree_node_write(struct bch_fs *c, struct btree *b, unsigned flags)