linux-kernel - [PATCH 13/13] block: don't check for BIO_MAX_PAGES in blk_bio_segment

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Message-ID: <149369654638.5146.3067734913419940612.stgit@noble>
Date:   Tue, 02 May 2017 13:42:26 +1000
From:   NeilBrown <neilb@...e.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, Ming Lei <tom.leiming@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 13/13] block: don't check for BIO_MAX_PAGES in
 blk_bio_segment_split()

blk_bio_segment_split() makes sure bios have no more than
BIO_MAX_PAGES entries in the bi_io_vec.
This was done because bio_clone_bioset() (when given a
mempool bioset) could not handle larger io_vecs.

No driver uses bio_clone_bioset() any more, they all
use bio_clone_fast() if anything, and bio_clone_fast()
doesn't clone the bi_io_vec.

The main user of of bio_clone_bioset() at this level
is bounce.c, and bouncing now happens before blk_bio_segment_split(),
so that is not of concern.

So remove the big helpful comment and the code.

Signed-off-by: NeilBrown <neilb@...e.com>
---
 block/blk-merge.c |   16 ----------------
 1 file changed, 16 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index e7862e9dcc39..cea544ec5d96 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -108,25 +108,9 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 	bool do_split = true;
 	struct bio *new = NULL;
 	const unsigned max_sectors = get_max_io_size(q, bio);
-	unsigned bvecs = 0;
 
 	bio_for_each_segment(bv, bio, iter) {
 		/*
-		 * With arbitrary bio size, the incoming bio may be very
-		 * big. We have to split the bio into small bios so that
-		 * each holds at most BIO_MAX_PAGES bvecs because
-		 * bio_clone_bioset() can fail to allocate big bvecs.
-		 *
-		 * Those drivers which will need to use bio_clone_bioset()
-		 * should tell us in some way.  For now, impose the
-		 * BIO_MAX_PAGES limit on all queues.
-		 *
-		 * TODO: handle users of bio_clone_bioset() differently.
-		 */
-		if (bvecs++ >= BIO_MAX_PAGES)
-			goto split;
-
-		/*
 		 * If the queue doesn't support SG gaps and adding this
 		 * offset would create a gap, disallow it.
 		 */