[PATCH] nvme_core: scan namespaces asynchronously

[Keith Busch]

On Thu, Jan 04, 2024 at 10:38:26AM -0600, Stuart Hayes wrote:
> Currently NVME namespaces are scanned serially, so it can take a long time
> for all of a controller's namespaces to become available, especially with a
> slower (fabrics) interface with large number (~1000) of namespaces.
> 
> Use async function calls to make namespace scanning happen in parallel,
> and add a (boolean) module parameter "async_ns_scan" to enable this.

Hm, we're not doing a whole lot of blocking IO to bring up a namespace,
so I'm a little surprised it makes a noticable difference. How much time
improvement are you observing by parallelizing the scan? Is there a
tipping point in Number of Namespaces where inline scanning is better
than asynchronous? And if it is a meaningful gain, let's not introduce
another module parameter to disable it.