linux-kernel - [PATCH v1 12/54] dm: limit the max bio size as BIO_MAX_PAGES * PAGE

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Date:   Tue, 27 Dec 2016 23:56:01 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org
Cc:     linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
        Ming Lei <tom.leiming@...il.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        dm-devel@...hat.com (maintainer:DEVICE-MAPPER (LVM)),
        Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org (open list:SOFTWARE RAID (Multiple Disks)
        SUPPORT)
Subject: [PATCH v1 12/54] 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.

Signed-off-by: Ming Lei <tom.leiming@...il.com>
---
 drivers/md/dm.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 3086da5664f3..6139bf7623f7 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -899,7 +899,16 @@ 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;
 }
-- 
2.7.4