On 4/25/19 2:41 AM, Ming Lei wrote:
On Thu, Apr 25, 2019 at 06:14:22AM +0800, Ming Lei wrote:
On Wed, Apr 24, 2019 at 10:20:46AM -0700, Sagi Grimberg wrote:
per-queue bioset is used originally for avoiding deadlock, are you
sure the static bioset is safe?
Can you explain this? I didn't find any indication of that in the change
log history...
Originally introduced by Kent:
bio split can be run from stacking drivers, for example, MD over NVMe,
if the global reserved mempool is consumed by MD bio splitting, then
no any progress can be made when splitting on bio submitted to NVMe.
Kent may have more details...
I guess it might be fine to use one shared global bio_set for all
lowest underlying queues, could be all queues except for loop, dm, md
, drbd, bcache, ...
But wasn't the overall idea of stacking drivers that we propagate the
queue limits up to the uppermost drivers, so that we have to do a split
only at the upper layers?
Furthermore, it's not every bio which needs to be split, only those
which straddle some device limitations.
The only ones not being able to propagate the queue limits is MD, and
that is already using a private bio_set here.
I've worked on a patchset to provide a separate bio set for each of the
stacking drivers, but the interface I've been able to come up with is
not very nice, and I really doubt it's worth it.
So I'd advocate to test with this patch first, and only provide
individual biosets once we find it's an issue.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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