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, 10 insertions, 0 deletions

diff --git a/fs/bcachefs/data_update.c b/fs/bcachefs/data_update.c
index 82d7e13e61a5..c3f12b3adb14 100644
--- a/fs/bcachefs/data_update.c
+++ b/fs/bcachefs/data_update.c
@@ -303,6 +303,13 @@ void bch2_data_update_read_done(struct data_update *m,
 void bch2_data_update_exit(struct data_update *update)
 {
 	struct bch_fs *c = update->op.c;
+	struct bkey_ptrs_c ptrs =
+		bch2_bkey_ptrs_c(bkey_i_to_s_c(update->k.k));
+	const struct bch_extent_ptr *ptr;
+
+	bkey_for_each_ptr(ptrs, ptr)
+		bch2_bucket_nocow_unlock(&c->nocow_locks,
+				       PTR_BUCKET_POS(c, ptr), 0);
 
 	bch2_bkey_buf_exit(&update->k, c);
 	bch2_disk_reservation_put(c, &update->op.res);
@@ -451,6 +458,9 @@ int bch2_data_update_init(struct bch_fs *c, struct data_update *m,
 			m->op.incompressible = true;
 
 		i++;
+
+		bch2_bucket_nocow_lock(&c->nocow_locks,
+				       PTR_BUCKET_POS(c, &p.ptr), 0);
 	}
 
 	if (reserve_sectors) {