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, 8 insertions, 2 deletions

diff --git a/fs/bcachefs/bcachefs.h b/fs/bcachefs/bcachefs.h
index 6d048e5d8843..74632105fb45 100644
--- a/fs/bcachefs/bcachefs.h
+++ b/fs/bcachefs/bcachefs.h
@@ -206,6 +206,7 @@
 #include "bcachefs_format.h"
 #include "errcode.h"
 #include "fifo.h"
+#include "nocow_locking.h"
 #include "opts.h"
 #include "util.h"
 
@@ -383,7 +384,8 @@ BCH_DEBUG_PARAMS_DEBUG()
 	x(journal_flush_seq)			\
 	x(blocked_journal)			\
 	x(blocked_allocate)			\
-	x(blocked_allocate_open_bucket)
+	x(blocked_allocate_open_bucket)		\
+	x(nocow_lock_contended)
 
 enum bch_time_stats {
 #define x(name) BCH_TIME_##name,
@@ -483,6 +485,7 @@ struct bch_dev {
 	struct bch_sb		*sb_read_scratch;
 	int			sb_write_error;
 	dev_t			dev;
+	atomic_t		flush_seq;
 
 	struct bch_devs_mask	self;
 
@@ -897,7 +900,9 @@ struct bch_fs {
 	struct bio_set		bio_read_split;
 	struct bio_set		bio_write;
 	struct mutex		bio_bounce_pages_lock;
-mempool_t		bio_bounce_pages;
+	mempool_t		bio_bounce_pages;
+	struct bucket_nocow_lock_table
+				nocow_locks;
 	struct rhashtable	promote_table;
 
 	mempool_t		compression_bounce[2];
@@ -959,6 +964,7 @@ mempool_t		bio_bounce_pages;
 	struct bio_set		writepage_bioset;
 	struct bio_set		dio_write_bioset;
 	struct bio_set		dio_read_bioset;
+	struct bio_set		nocow_flush_bioset;
 
 	/* ERRORS */
 	struct list_head	fsck_errors;