Patch "block: split bios to max possible length" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    block: split bios to max possible length

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     block-split-bios-to-max-possible-length.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From e36f6204288088fda50d1c84830340ccb70f85ff Mon Sep 17 00:00:00 2001
From: Keith Busch <keith.busch@intel.com>
Date: Tue, 12 Jan 2016 15:08:39 -0700
Subject: block: split bios to max possible length

From: Keith Busch <keith.busch@intel.com>

commit e36f6204288088fda50d1c84830340ccb70f85ff upstream.

This splits bio in the middle of a vector to form the largest possible
bio at the h/w's desired alignment, and guarantees the bio being split
will have some data.

The criteria for splitting is changed from the max sectors to the h/w's
optimal sector alignment if it is provided. For h/w that advertise their
block storage's underlying chunk size, it's a big performance win to not
submit commands that cross them. If sector alignment is not provided,
this patch uses the max sectors as before.

This addresses the performance issue commit d380561113 attempted to
fix, but was reverted due to splitting logic error.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 block/blk-merge.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -81,9 +81,6 @@ static struct bio *blk_bio_segment_split
 	struct bio *new = NULL;
 
 	bio_for_each_segment(bv, bio, iter) {
-		if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q))
-			goto split;
-
 		/*
 		 * If the queue doesn't support SG gaps and adding this
 		 * offset would create a gap, disallow it.
@@ -91,6 +88,22 @@ static struct bio *blk_bio_segment_split
 		if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
 			goto split;
 
+		if (sectors + (bv.bv_len >> 9) >
+				blk_max_size_offset(q, bio->bi_iter.bi_sector)) {
+			/*
+			 * Consider this a new segment if we're splitting in
+			 * the middle of this vector.
+			 */
+			if (nsegs < queue_max_segments(q) &&
+			    sectors < blk_max_size_offset(q,
+						bio->bi_iter.bi_sector)) {
+				nsegs++;
+				sectors = blk_max_size_offset(q,
+						bio->bi_iter.bi_sector);
+			}
+			goto split;
+		}
+
 		if (bvprvp && blk_queue_cluster(q)) {
 			if (seg_size + bv.bv_len > queue_max_segment_size(q))
 				goto new_segment;


Patches currently in stable-queue which might be from keith.busch@intel.com are

queue-4.4/block-split-bios-to-max-possible-length.patch