ACK: [SRU][Xenial][Yakkety][PATCH 1/1] block: relax check on sg gap

[Seth Forshee]

On Thu, Apr 13, 2017 at 06:45:15AM -0400, Joseph Salisbury wrote:
> From: Ming Lei <ming.lei at canonical.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1682215
> 
> If the last bvec of the 1st bio and the 1st bvec of the next
> bio are physically contigious, and the latter can be merged
> to last segment of the 1st bio, we should think they don't
> violate sg gap(or virt boundary) limit.
> 
> Both Vitaly and Dexuan reported lots of unmergeable small bios
> are observed when running mkfs on Hyper-V virtual storage, and
> performance becomes quite low. This patch fixes that performance
> issue.
> 
> The same issue should exist on NVMe, since it sets virt boundary too.
> 
> Reported-by: Vitaly Kuznetsov <vkuznets at redhat.com>
> Reported-by: Dexuan Cui <decui at microsoft.com>
> Tested-by: Dexuan Cui <decui at microsoft.com>
> Cc: Keith Busch <keith.busch at intel.com>
> Signed-off-by: Ming Lei <ming.lei at canonical.com>
> Signed-off-by: Jens Axboe <axboe at fb.com>
> (cherry picked from commit 729204ef49ec00b788ce23deb9eb922a5769f55d)
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>

Clean cherry pick, positive test results.

Acked-by: Seth Forshee <seth.forshee at canonical.com>