bcachefs: Make IO in flight by copygc/rebalance configurable

This adds a new option, move_bytes_in_flight, for configuring the amount
of IO in flight by copygc/rebalance - users with many devices in their
filesystem will want to increase this.

In the future we should be smarter about this, but this is an easy
improvement.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/move.c

@@ -22,8 +22,6 @@
 #include <linux/ioprio.h>
 #include <linux/kthread.h>
 
-#define SECTORS_IN_FLIGHT_PER_DEVICE	2048
-
 struct moving_io {
 	struct list_head	list;
 	struct closure		cl;
@@ -693,11 +691,11 @@ static int __bch2_move_data(struct bch_fs *c,
 
 		move_ctxt_wait_event(ctxt, &trans,
 			atomic_read(&ctxt->write_sectors) <
-			SECTORS_IN_FLIGHT_PER_DEVICE);
+			c->opts.move_bytes_in_flight >> 9);
 
 		move_ctxt_wait_event(ctxt, &trans,
 			atomic_read(&ctxt->read_sectors) <
-			SECTORS_IN_FLIGHT_PER_DEVICE);
+			c->opts.move_bytes_in_flight >> 9);
 
 		bch2_trans_begin(&trans);
 

fs/bcachefs/opts.h

@@ -290,6 +290,11 @@ enum opt_type {
 	  OPT_UINT(0, U32_MAX),						\
 	  BCH_SB_JOURNAL_RECLAIM_DELAY,	100,				\
 	  NULL,		"Delay in milliseconds before automatic journal reclaim")\
+	x(move_bytes_in_flight,		u32,				\
+	  OPT_HUMAN_READABLE|OPT_FS|OPT_MOUNT|OPT_RUNTIME,		\
+	  OPT_UINT(1024, U32_MAX),					\
+	  BCH2_NO_SB_OPT,		1U << 20,			\
+	  NULL,		"Amount of IO in flight to keep in flight by the move path")\
 	x(fsck,				u8,				\
 	  OPT_FS|OPT_MOUNT,						\
 	  OPT_BOOL(),							\