bcachefs: Don't require flush/fua on every journal write

This patch adds a flag to journal entries which, if set, indicates that
they weren't done as flush/fua writes.

 - non flush/fua journal writes don't update last_seq (i.e. they don't
   free up space in the journal), thus the journal free space
   calculations now check whether nonflush journal writes are currently
   allowed (i.e. are we low on free space, or would doing a flush write
   free up a lot of space in the journal)

 - write_delay_ms, the user configurable option for when open journal
   entries are automatically written, is now interpreted as the max
   delay between flush journal writes (default 1 second).

 - bch2_journal_flush_seq_async is changed to ensure a flush write >=
   the requested sequence number has happened

 - journal read/replay must now ignore, and blacklist, any journal
   entries newer than the most recent flush entry in the journal. Also,
   the way the read_entire_journal option is handled has been improved;
   struct journal_replay now has an entry, 'ignore', for entries that
   were read but should not be used.

 - assorted refactoring and improvements related to journal read in
   journal_io.c and recovery.c

Previously, we'd have to issue a flush/fua write every time we
accumulated a full journal entry - typically the bucket size. Now we
need to issue them much less frequently: when an fsync is requested, or
it's been more than write_delay_ms since the last flush, or when we need
to free up space in the journal. This is a significant performance
improvement on many write heavy workloads.

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

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/bcachefs/journal_types.h b/fs/bcachefs/journal_types.h
index 6b525dc6ab7c..cf9675310f2b 100644
--- a/fs/bcachefs/journal_types.h
+++ b/fs/bcachefs/journal_types.h
@@ -29,6 +29,8 @@ struct journal_buf {
 	unsigned		disk_sectors;	/* maximum size entry could have been, if
 						   buf_size was bigger */
 	unsigned		u64s_reserved;
+	bool			noflush;	/* write has already been kicked off, and was noflush */
+	bool			must_flush;	/* something wants a flush */
 	/* bloom filter: */
 	unsigned long		has_inode[1024 / sizeof(unsigned long)];
 };
@@ -146,6 +148,7 @@ enum {
 	JOURNAL_RECLAIM_STARTED,
 	JOURNAL_NEED_WRITE,
 	JOURNAL_MAY_GET_UNRESERVED,
+	JOURNAL_MAY_SKIP_FLUSH,
 };
 
 /* Embedded in struct bch_fs */
@@ -203,6 +206,7 @@ struct journal {
 
 	/* seq, last_seq from the most recent journal entry successfully written */
 	u64			seq_ondisk;
+	u64			flushed_seq_ondisk;
 	u64			last_seq_ondisk;
 	u64			err_seq;
 	u64			last_empty_seq;
@@ -252,11 +256,15 @@ struct journal {
 
 	unsigned		write_delay_ms;
 	unsigned		reclaim_delay_ms;
+	unsigned long		last_flush_write;
 
 	u64			res_get_blocked_start;
 	u64			need_write_time;
 	u64			write_start_time;
 
+	u64			nr_flush_writes;
+	u64			nr_noflush_writes;
+
 	struct bch2_time_stats	*write_time;
 	struct bch2_time_stats	*delay_time;
 	struct bch2_time_stats	*blocked_time;