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Re: [PATCH 03/24] nvme: let set_capacity_revalidate_and_notify update the bdev size

On 11/10/20 12:28 AM, Sagi Grimberg wrote:

[ .. ]
Originally nvme multipath would update/change the size of the multipath
device according to the underlying path devices.
With this patch the size of the multipath device will _not_ change if there
is a change on the underlying devices.

Yes, it will.  Take a close look at nvme_update_disk_info and how it is

Okay, then: What would be the correct way of handling a size update for NVMe multipath?
Assuming we're getting an AEN for each path signalling the size change
(or a controller reset leading to a size change).
So if we're updating the size of the multipath device together with the path device at the first AEN/reset we'll end up with the other paths having a different size than the multipath device (and the path we've just been updating).
- Do we care, or cross fingers and hope for the best?
- Shouldn't we detect the case where we won't get a size update for the other paths, or, indeed, we have a genuine device size mismatch due to a misconfiguration on the target?

IE shouldn't we have a flag 'size update pending' for the other paths,, to take them out ouf use temporarily until the other AENs/resets have been processed?

the mpath device will take the minimum size from all the paths, that is
what blk_stack_limits does. When the AEN for all the paths will arrive
the mpath size will update.

But that's precisely my point; there won't be an AEN for _all_ paths, but rather one AEN per path. Which will be processed separately, leading to the issue described above.

Not sure how this is different than what we have today...

Oh, that is a problem even today.
So we should probably move it to a different thread...


Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
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