[Devel] [RH7 PATCH 3/6] ploop: add delayed flush support

[Dmitry Monakhov]

dio_submit and dio_submit_pad may produce several bios. This makes
processing of REQ_FUA complicated because in order to preserve correctness
we have to TAG each bio with FUA flag which is suboptimal.
Obviously there is a room for optimization here: once all bios was acknowledged
by lower layer we may issue empty barrier aka ->issue_flush().
post_submit call back is the place where we all bios completed already.

b1:FUA, b2:FUA, b3:FUA =>  b1,b2,b3,wait_for_bios,bX:FLUSH

This allow us to remove all this REQ_FORCE_{FLUSH,FUA} crap and

Signed-off-by: Dmitry Monakhov <dmonakhov at openvz.org>
---
 drivers/block/ploop/io_direct.c | 48 +++++++++++++++++------------------------
 include/linux/ploop/ploop.h     |  2 ++
 2 files changed, 22 insertions(+), 28 deletions(-)

diff --git a/drivers/block/ploop/io_direct.c b/drivers/block/ploop/io_direct.c
index 195d318..752a9c3e 100644
--- a/drivers/block/ploop/io_direct.c
+++ b/drivers/block/ploop/io_direct.c
@@ -82,31 +82,13 @@ dio_submit(struct ploop_io *io, struct ploop_request * preq,
 	sector_t sec, nsec;
 	int err;
 	struct bio_list_walk bw;
-	int preflush;
-	int postfua = 0;
+	int preflush = !!(rw & REQ_FLUSH);
+	int postflush = !!(rw & REQ_FUA);
 	int write = !!(rw & REQ_WRITE);
 
 	trace_submit(preq);
 
-	preflush = !!(rw & REQ_FLUSH);
-
-	if (test_and_clear_bit(PLOOP_REQ_FORCE_FLUSH, &preq->state))
-		preflush = 1;
-
-	if (test_and_clear_bit(PLOOP_REQ_FORCE_FUA, &preq->state))
-		postfua = 1;
-
-	if (!postfua && ploop_req_delay_fua_possible(rw, preq)) {
-
-		/* Mark req that delayed flush required */
-		set_bit(PLOOP_REQ_FORCE_FLUSH, &preq->state);
-	} else if (rw & REQ_FUA) {
-		postfua = 1;
-	}
-
 	rw &= ~(REQ_FLUSH | REQ_FUA);
-
-
 	bio_list_init(&bl);
 
 	if (iblk == PLOOP_ZERO_INDEX)
@@ -237,13 +219,14 @@ flush_bio:
 			rw2 |= REQ_FLUSH;
 			preflush = 0;
 		}
-		if (unlikely(postfua && !bl.head))
-			rw2 |= REQ_FUA;
-
 		ploop_acc_ff_out(preq->plo, rw2 | b->bi_rw);
 		submit_bio(rw2, b);
 	}
-
+	/* TODO: minor optimization is possible for single bio case */
+	if (postflush) {
+		set_bit(PLOOP_REQ_DEL_FLUSH, &preq->state);
+		ploop_add_post_submit(io, preq);
+	}
 	ploop_complete_io_request(preq);
 	return;
 
@@ -523,9 +506,10 @@ dio_convert_extent(struct ploop_io *io, struct ploop_request * preq)
 					      (loff_t)sec << 9, clu_siz);
 
 	/* highly unlikely case: FUA coming to a block not provisioned yet */
-	if (!err && force_sync)
+	if (!err && force_sync) {
+		clear_bit(PLOOP_REQ_DEL_FLUSH, &preq->state);
 		err = io->ops->sync(io);
-
+	}
 	if (!force_sync) {
 		spin_lock_irq(&plo->lock);
 		io->io_count++;
@@ -546,7 +530,12 @@ dio_post_submit(struct ploop_io *io, struct ploop_request * preq)
 	if (test_and_clear_bit(PLOOP_REQ_DEL_CONV, &preq->state))
 		dio_convert_extent(io, preq);
 
+	if (test_and_clear_bit(PLOOP_REQ_DEL_FLUSH, &preq->state)) {
+		io->ops->issue_flush(io, preq);
+		return 1;
+	}
 	return 0;
+
 }
 
 /* Submit the whole cluster. If preq contains only partial data
@@ -562,7 +551,6 @@ dio_submit_pad(struct ploop_io *io, struct ploop_request * preq,
 	sector_t sec, end_sec, nsec, start, end;
 	struct bio_list_walk bw;
 	int err;
-
 	bio_list_init(&bl);
 
 	/* sec..end_sec is the range which we are going to write */
@@ -694,7 +682,11 @@ flush_bio:
 		ploop_acc_ff_out(preq->plo, rw | b->bi_rw);
 		submit_bio(rw, b);
 	}
-
+	/* TODO: minor optimization is possible for single bio case */
+	if (preq->req_rw &  REQ_FUA) {
+		set_bit(PLOOP_REQ_DEL_FLUSH, &preq->state);
+		ploop_add_post_submit(io, preq);
+	}
 	ploop_complete_io_request(preq);
 	return;
 
diff --git a/include/linux/ploop/ploop.h b/include/linux/ploop/ploop.h
index 4c52a40..5076f16 100644
--- a/include/linux/ploop/ploop.h
+++ b/include/linux/ploop/ploop.h
@@ -472,6 +472,7 @@ enum
 	PLOOP_REQ_PUSH_BACKUP, /* preq was ACKed by userspace push_backup */
 	PLOOP_REQ_ALLOW_READS, /* READs are allowed for given req_cluster */
 	PLOOP_REQ_DEL_CONV,    /* post_submit: conversion required */
+	PLOOP_REQ_DEL_FLUSH,   /* post_submit: REQ_FLUSH required */
 	PLOOP_REQ_FSYNC_DONE,  /* fsync_thread() performed f_op->fsync() */
 };
 
@@ -482,6 +483,7 @@ enum
 #define PLOOP_REQ_ZERO_FL (1 << PLOOP_REQ_ZERO)
 #define PLOOP_REQ_POST_SUBMIT_FL (1 << PLOOP_REQ_POST_SUBMIT)
 #define PLOOP_REQ_DEL_CONV_FL (1 << PLOOP_REQ_DEL_CONV)
+#define PLOOP_REQ_DEL_FLUSH_FL (1 << PLOOP_REQ_DEL_FLUSH)
 
 enum
 {
-- 
1.8.3.1