Re: [PATCH v1 12/54] dm: limit the max bio size as BIO_MAX_PAGES * PAGE_SIZE

On Wed, Jan 4, 2017 at 12:43 AM, Mike Snitzer [off-list ref] wrote:

On Tue, Dec 27 2016 at 10:56am -0500,
Ming Lei [off-list ref] wrote:

quoted

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@gmail.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

dm_set_target_max_io_len() is already meant to be called by the .ctr
hook for each DM target.  So why not just have the dm-crypt target (and
other targets if needed) pass your reduced $len?

That way only targets that need to be fixed (e.g. dm-crypt) impose this
limit.

Looks better way, and I will do it in V2.


Thanks,
Ming Lei