On 4/25/19 5:36 PM, Ming Lei wrote:
On Thu, Apr 25, 2019 at 04:32:42PM +0200, Hannes Reinecke wrote:
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?
For example, LVM over RAID, the limits of LVM queue is figured out and fixed
during creating LVM. However, new device may be added to the RAID. Then the
underlying queue's limit may not be propagated to LVM's queue's limit.
And we did discuss the topic of 'block: dm: restack queue_limits'
before, looks not see any progress made.
Also loop doesn't consider stack limits at all.
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.
If DM and the lowest queue share one same bio_set(mem_pool), it isn't
enough for MD to use private bio_set.
Ah, right. I've reviewed the patches implementing the per-queue biosets,
and indeed we'll need to use them.
But meanwhile I've found another way of circumventing this issue, so
this patch can be dropped.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
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