linux-kernel - [PATCH V4 06/45] dm: limit the max bio size as BIO_MAX_PAGES * PAGE

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Date:   Mon, 18 Dec 2017 20:22:08 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Jens Axboe <axboe@...com>, Christoph Hellwig <hch@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Kent Overstreet <kent.overstreet@...il.com>
Cc:     Huang Ying <ying.huang@...el.com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, Theodore Ts'o <tytso@....edu>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Coly Li <colyli@...e.de>, Filipe Manana <fdmanana@...il.com>,
        Ming Lei <ming.lei@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH V4 06/45] dm: limit the max bio size as BIO_MAX_PAGES * PAGE_SIZE

For BIO based DM, some targets aren't ready for dealing with bigger
incoming bio than 1Mbyte, such as crypt target.

Cc: Mike Snitzer <snitzer@...hat.com>
Cc:dm-devel@...hat.com
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
---
 drivers/md/dm.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index de17b7193299..7475739fee49 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -920,7 +920,15 @@ int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)
 		return -EINVAL;
 	}
 
-	ti->max_io_len = (uint32_t) len;
+	/*
+	 * BIO based queue uses its own splitting. When multipage bvecs
+	 * is switched on, size of the incoming bio may be too big to
+	 * be handled in some targets, such as crypt.
+	 *
+	 * When these targets are ready for the big bio, we can remove
+	 * the limit.
+	 */
+	ti->max_io_len = min_t(uint32_t, len, BIO_MAX_PAGES * PAGE_SIZE);
 
 	return 0;
 }
-- 
2.9.5