linux-kernel - Re: [PATCH 01/10] block: make generic_make

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Date:	Tue, 05 May 2015 23:08:20 -0700
From:	Ming Lin <mlin@...nel.org>
To:	Christoph Hellwig <hch@....de>
CC:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Dongsu Park <dongsu.park@...fitbricks.com>,
	Christoph Hellwig <hch@...radead.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Ming Lei <ming.lei@...onical.com>, Neil Brown <neilb@...e.de>,
	Alasdair Kergon <agk@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
	Lars Ellenberg <drbd-dev@...ts.linbit.com>,
	drbd-user@...ts.linbit.com, Jiri Kosina <jkosina@...e.cz>,
	Geoff Levand <geoff@...radead.org>, Jim Paris <jim@...n.com>,
	Joshua Morris <josh.h.morris@...ibm.com>,
	Philip Kelleher <pjk1939@...ux.vnet.ibm.com>,
	Minchan Kim <minchan@...nel.org>,
	Nitin Gupta <ngupta@...are.org>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Andreas Dilger <andreas.dilger@...el.com>,
	Keith Busch <keith.busch@...el.com>
Subject: Re: [PATCH 01/10] block: make generic_make_request handle arbitrarily
 sized bios

On 04/28/2015 04:43 AM, Christoph Hellwig wrote:
> This seems to lack support for QUEUE_FLAG_SG_GAPS to work around
> the retarded PPR format in the NVMe driver.  I'm actually not
> sure we have a way to reproduce them for BLOCK_PC requests, but I think
> we should make sure to properly handle them.

How about below incremental patch?

 block/bio.c       | 8 --------
 block/blk-merge.c | 8 ++++++++
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index ae31cdb..3f6bd9a 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -743,14 +743,6 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
 			bio->bi_iter.bi_size += len;
 			goto done;
 		}
-
-		/*
-		 * If the queue doesn't support SG gaps and adding this
-		 * offset would create a gap, disallow it.
-		 */
-		if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS) &&
-		    bvec_gap_to_prev(prev, offset))
-			return 0;
 	}
 
 	if (bio->bi_vcnt >= bio->bi_max_vecs)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 9d565a0..32f6d6c 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -78,6 +78,14 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 		if (sectors > queue_max_sectors(q))
 			goto split;
 
+		/*
+		 * If the queue doesn't support SG gaps and adding this
+		 * offset would create a gap, disallow it.
+		 */
+		if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS) &&
+		    prev && bvec_gap_to_prev(&bvprv, bv.bv_offset))
+			goto split;
+
 		if (prev && blk_queue_cluster(q)) {
 			if (seg_size + bv.bv_len > queue_max_segment_size(q))
 				goto new_segment;

--
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