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

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)

Yes and no.

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


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