[dm-devel] [PATCH] Respect REQ_NOWATI bios

[Mikulas Patocka]

Hi

Here I'm sending that patch for REQ_NOWAIT for review.

It is not tested, except for some trivial tests that involve logical 
volume activation.

I found out that it seems easier to propagate the error using bits in 
clone_info rather than changing return codes for each affected function.

Mikulas


Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

---
 drivers/md/dm.c |   51 +++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 45 insertions(+), 6 deletions(-)

Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c
+++ linux-2.6/drivers/md/dm.c
@@ -87,6 +87,8 @@ struct clone_info {
 	unsigned int sector_count;
 	bool is_abnormal_io:1;
 	bool submit_as_polled:1;
+	bool is_nowait:1;
+	bool nowait_failed:1;
 };
 
 static inline struct dm_target_io *clone_to_tio(struct bio *clone)
@@ -570,13 +572,21 @@ static void dm_end_io_acct(struct dm_io
 	dm_io_acct(io, true);
 }
 
-static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio)
+static struct dm_io *alloc_io(struct clone_info *ci, struct mapped_device *md, struct bio *bio)
 {
 	struct dm_io *io;
 	struct dm_target_io *tio;
 	struct bio *clone;
 
-	clone = bio_alloc_clone(NULL, bio, GFP_NOIO, &md->mempools->io_bs);
+	if (unlikely(ci->is_nowait)) {
+		clone = bio_alloc_clone(NULL, bio, GFP_NOWAIT, &md->mempools->io_bs);
+		if (!clone) {
+			ci->nowait_failed = true;
+			return NULL;
+		}
+	} else {
+		clone = bio_alloc_clone(NULL, bio, GFP_NOIO, &md->mempools->io_bs);
+	}
 	tio = clone_to_tio(clone);
 	tio->flags = 0;
 	dm_tio_set_flag(tio, DM_TIO_INSIDE_DM_IO);
@@ -1503,6 +1513,11 @@ static void alloc_multiple_bios(struct b
 
 		while ((bio = bio_list_pop(blist)))
 			free_tio(bio);
+
+		if (ci->is_nowait) {
+			ci->nowait_failed = true;
+			return;
+		}
 	}
 }
 
@@ -1519,7 +1534,15 @@ static unsigned int __send_duplicate_bio
 	case 1:
 		if (len)
 			setup_split_accounting(ci, *len);
-		clone = alloc_tio(ci, ti, 0, len, GFP_NOIO);
+		if (unlikely(ci->is_nowait)) {
+			clone = alloc_tio(ci, ti, 0, len, GFP_NOWAIT);
+			if (!clone) {
+				ci->nowait_failed = true;
+				return 0;
+			}
+		} else {
+			clone = alloc_tio(ci, ti, 0, len, GFP_NOIO);
+		}
 		__map_bio(clone);
 		ret = 1;
 		break;
@@ -1656,7 +1679,7 @@ static blk_status_t __process_abnormal_i
 
 	__send_changing_extent_only(ci, ti, num_bios,
 				    max_granularity, max_sectors);
-	return BLK_STS_OK;
+	return likely(!ci->nowait_failed) ? BLK_STS_OK : BLK_STS_AGAIN;
 }
 
 /*
@@ -1729,7 +1752,15 @@ static blk_status_t __split_and_process_
 
 	len = min_t(sector_t, max_io_len(ti, ci->sector), ci->sector_count);
 	setup_split_accounting(ci, len);
-	clone = alloc_tio(ci, ti, 0, &len, GFP_NOIO);
+	if (unlikely(ci->is_nowait)) {
+		clone = alloc_tio(ci, ti, 0, &len, GFP_NOWAIT);
+		if (unlikely(!clone)) {
+			ci->nowait_failed = true;
+			return BLK_STS_AGAIN;
+		}
+	} else {
+		clone = alloc_tio(ci, ti, 0, &len, GFP_NOIO);
+	}
 	__map_bio(clone);
 
 	ci->sector += len;
@@ -1741,8 +1772,10 @@ static blk_status_t __split_and_process_
 static void init_clone_info(struct clone_info *ci, struct mapped_device *md,
 			    struct dm_table *map, struct bio *bio, bool is_abnormal)
 {
+	ci->is_nowait = !!(bio->bi_opf & REQ_NOWAIT);
+	ci->nowait_failed = false;
 	ci->map = map;
-	ci->io = alloc_io(md, bio);
+	ci->io = alloc_io(ci, md, bio);
 	ci->bio = bio;
 	ci->is_abnormal_io = is_abnormal;
 	ci->submit_as_polled = false;
@@ -1778,10 +1811,16 @@ static void dm_split_and_process_bio(str
 	}
 
 	init_clone_info(&ci, md, map, bio, is_abnormal);
+	if (unlikely(ci.nowait_failed)) {
+		error = BLK_STS_AGAIN;
+		goto out;
+	}
 	io = ci.io;
 
 	if (bio->bi_opf & REQ_PREFLUSH) {
 		__send_empty_flush(&ci);
+		if (unlikely(ci.nowait_failed))
+			error = BLK_STS_AGAIN;
 		/* dm_io_complete submits any data associated with flush */
 		goto out;
 	}