Re: [Xen-devel] PVH dom0 creation fails - the system freezes

[<bercarug@xxxxxxxxxx>]

On 07/25/2018 07:12 PM, Roger Pau Monné wrote:
> On Wed, Jul 25, 2018 at 05:05:35PM +0300, bercarug@xxxxxxxxxx wrote:
> > On 07/25/2018 05:02 PM, Wei Liu wrote:
> > > On Wed, Jul 25, 2018 at 03:41:11PM +0200, Juergen Gross wrote:
> > > > On 25/07/18 15:35, Roger Pau Monné wrote:
> > > > > > What could be causing the available memory loss problem?
> > > > > That seems to be Linux aggressively ballooning out memory, you go from
> > > > > 7129M total memory to 246M. Are you creating a lot of domains?
> > > > This might be related to the tools thinking dom0 is a PV domain.
> > > Good point.
> > >
> > > In that case, xenstore-ls -fp would also be useful. The output should
> > > show the balloon target for Dom0.
> > >
> > > You can also try to set the autoballoon to off in /etc/xen/xl.cfg to see
> > > if it makes any difference.
> > >
> > > Wei.
> > Also tried setting autoballooning off, but it had no effect.
> This is a Linux/libxl issue that I'm not sure what's the best way to
> solve. Linux has the following 'workaround' in the balloon driver:
>
> err = xenbus_scanf(XBT_NIL, "memory", "static-max", "%llu",
>                    &static_max);
> if (err != 1)
>         static_max = new_target;
> else
>         static_max >>= PAGE_SHIFT - 10;
> target_diff = xen_pv_domain() ? 0
>                 : static_max - balloon_stats.target_pages;
>
> I suppose this is used to cope with the memory reporting mismatch
> usually seen on HVM guests. This however interacts quite badly on a
> PVH Dom0 that has for example:
>
> /local/domain/0/memory/target = "8391840"   (n0)
> /local/domain/0/memory/static-max = "17179869180"   (n0)
>
> One way to solve this is to set target and static-max to the same
> value initially, so that target_diff on Linux is 0. Another option
> would be to force target_diff = 0 for Dom0.
>
> I'm attaching a patch for libxl that should solve this, could you
> please give it a try and report back?
>
> I'm still unsure however about the best way to fix this, need to think
> about it.
>
> Roger.
> ---8<---
> diff --git a/tools/libxl/libxl_mem.c b/tools/libxl/libxl_mem.c
> index e551e09fed..2c984993d8 100644
> --- a/tools/libxl/libxl_mem.c
> +++ b/tools/libxl/libxl_mem.c
> @@ -151,7 +151,9 @@ retry_transaction:
>           *target_memkb = info.current_memkb;
>       }
>       if (staticmax == NULL) {
> -        libxl__xs_printf(gc, t, max_path, "%"PRIu64, info.max_memkb);
> +        libxl__xs_printf(gc, t, max_path, "%"PRIu64,
> +                         libxl__domain_type(gc, 0) == LIBXL_DOMAIN_TYPE_PV ?
> +                         info.max_memkb : info.current_memkb);
>           *max_memkb = info.max_memkb;
>       }
>   
I have tried Roger's patch and it fixed the memory decrease problem. "xl 
list -l"
no longer causes any issue.

The output of "xenstore-ls -fp" shows that both target and static-max 
are now
set to the same value.


Gabriel




Amazon Development Center (Romania) S.R.L. registered office: 27A Sf. Lazar 
Street, UBC5, floor 2, Iasi, Iasi County, 700045, Romania. Registered in 
Romania. Registration number J22/2621/2005.
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