Re: [Xen-devel] xen-blkfront hang

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Aug 04, 2017 at 10:00:09AM +0200, Valentin Vidic wrote:
> On Mon, Jul 31, 2017 at 09:09:19AM +0800, Dongli Zhang wrote:
> > To verify whether the above patch would help, please check the 
> > nr_grant_frames
> > value in guest domU. If this value is exactly the same of maximum grant 
> > frames
> > (by default, xen mainline uses 32) and the number of free grant references 
> > is
> > very small, the above patch might help.
> 
> You are right, this is what I get after the machine hangs:
> 
>   crash> print nr_grant_frames 
>   $1 = 32
>   crash> print gnttab_free_count 
>   $2 = 9
> 
> > The best way is to increase the gnttab_max_frames to larger value (e.g.,  
> > 256)
> > in dom0 xen.gz grub.
> 
> Thank you, this seems to help.  The test machine does not hang now and
> the numbers are looking better now:
> 
>   crash> print nr_grant_frames 
>   $1 = 59
>   crash> print gnttab_free_count 
>   $2 = 356

At some point I've already expressed my opinion that having a
per-queue list of persistent grants was not a good idea. Now I think
the only solution is to remove persistent grants, or to lower the
default number of per-queue persistent grants to a ridiculously low
value.

Roger.

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