[dm-devel] [patch 5/5] block: use a driver-specific handler for the "inflight" value

[Mike Snitzer]

On Thu, Nov 08 2018 at  9:52am -0500,
Christoph Hellwig <hch at infradead.org> wrote:

> On Tue, Nov 06, 2018 at 10:35:03PM +0100, Mikulas Patocka wrote:
> > Device mapper was converted to percpu inflight counters. In order to
> > display the correct values in the "inflight" sysfs file, we need a custom
> > callback that sums the percpu counters.
> 
> The attribute that calls this is per-partition, while your method
> is per-queue, so there is some impedence mismatch here.
> 
> Is there any way you could look into just making the generic code
> use percpu counters?

Discussed doing that with Jens and reported as much here:

https://www.redhat.com/archives/dm-devel/2018-November/msg00068.html

And Jens gave additional context for why yet another attempt to switch
block core's in_flight to percpu counters is doomed (having already been
proposed and rejected twice):

https://www.redhat.com/archives/dm-devel/2018-November/msg00071.html

And yes, definitely should've cc'd linux-block (now added).

Mike