Re: USB umass hard drive "failed to create xfers" when attaching

[Nick Hudson <nick.hudson%gmx.co.uk@localhost>]

On 17/02/2020 16:23, Paul Goyette wrote:
[...]

> > More info...
> >
> > First, this is on a amd64 system, witwh 8core/16thread and 128GB of RAM.
> >
> > On IRC it was suggested (thanks, maya!) that the error message might be
> > related to memory fragmentation.  I didn't believe it (given how much
> > RAM I have), but a quick check with top(1) showed that I had more than
> > 100GB of 'file cache' active.  So, I unmounted all my development trees
> > (to force the cache to get flushed).  Sure enough, I am now able to
> > successfully mount the USB drive!
> >
> > So, sounds like "something somewhere isn't quite right (tm)".  I would
> > have expected a memory allocation failure to automatically trigger some
> > mechanism to reclaim some of the file cache...
>
> And, based on more discussion, this would seem to be a kernel virtual
> address fragmentation issue, and not related to physical memory being
> available.  The concensus on IRC is that this is a bug in the xhci(4)
> driver.

Yes and no.

xhci could do better and support multiple DMA segments, but uvm could
also help.

Nick