Re: [Xen-devel] Populate-on-demand memory problem

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

Sorry, I've been trying to test all of the p2m/pod patches on a machine 
with HAP (since some paches, like the one that enables replacing 4k 
pages with a superpage, can only be tested on HAP), and running into a 
bunch of problems.
But this patch can clearly stand on its own, so I'll post it later today.

 -George

On 09/08/10 10:29, Keir Fraser wrote:
> On 09/08/2010 09:48, "Jan Beulich"<JBeulich@xxxxxxxxxx>  wrote:
>
> > Keir,
> >
> > with Dietmar having tested this successfully, is there anything that
> > keeps this from being applied to -unstable (and perhaps also 4.0.1)?
> George needs to resubmit it for inclusion, with a proper changeset comment
> and a signed-off-by line.
>
>   -- Keir
>
> > Jan
> >
> > > > > On 27.07.10 at 15:10, George Dunlap<George.Dunlap@xxxxxxxxxxxxx>  wrote:
> > > Hmm, looks like I neglected to push a fix upstream.  Can you test it
> > > with the attached patch, and tell me if that fixes your problem?
> > >
> > >   -George
> > >
> > > On Tue, Jul 27, 2010 at 8:48 AM, Dietmar Hahn
> > > <dietmar.hahn@xxxxxxxxxxxxxx>  wrote:
> > > > Hi list,
> > > >
> > > > we ported our system from Novel SLES11 using xen-3.3 to SLES11 SP1 using
> > > > xen-4.0 and ran into some trouble with the pod stuff.
> > > > We have a HVM guest and already used target_mem<  max_mem on startup of
> > > > the guest.
> > > > With the new xen version we get
> > > > (XEN) p2m_pod_demand_populate: Out of populate-on-demand memory! tot_pages
> > > 792792 pod_entries 800
> > > > I did some code revisions and looking at pod patches
> > > > (http://lists.xensource.com/archives/html/xen-devel/2008-12/msg01030.html)
> > > > to understand the behavior. We use the following configuration:
> > > > maxmem = 4096
> > > > memory = 3096
> > > > What I see is:
> > > >   - our guest boots with e820 map showing maxmem.
> > > >   - reading xenstore memory/target returns '3170304' means 3096MB, 792576
> > > pages
> > > > Now our guest uses the target memory and gives back 1000MB via
> > > > hypervisor call XENMEM_decrease_reservation to the hypervisor.
> > > >
> > > > Later I try to map the complete domU memory into dom0 kernel space and here
> > > I
> > > > get the 'Out of populate-on-demand memory' crash.
> > > >
> > > > As far as I understand (ignoring the p2m_pod_emergency_sweep)
> > > > - on populating a page
> > > >    - the page is taken from the pod cache
> > > >    - p2md->pod.count--
> > > >    - p2md->pod.entry_count--
> > > >    - page gets type p2m_ram_rw
> > > > - decreasing a page
> > > >    - p2md->pod.entry_count--
> > > >    - page gets type p2m_invalid
> > > >
> > > > So if the guest uses all the target memory and gave back all
> > > > the (maxmem-target) memory p2md->pod.count and p2md->pod.entry_count should
> > > > be
> > > > zero.
> > > > I added some tracing in the hypervisor and see on start of the guest:
> > > > p2m_pod_set_cache_target: p2md->pod.count: 791264 tot_pages: 791744
> > > > This pod.count is lower then the target seen in the guest!
> > > > On the first call of p2m_pod_demand_populate() I can see
> > > > p2m_pod_demand_populate: p2md->pod.entry_count: 1048064 p2md->pod.count:
> > > > 791264
> > > tot_pages: 792792
> > > > So pod.entry_count=1048064 (4096MB) complies to maxmem but
> > > > pod.count=791264 is lower then the target memory in xenstore.
> > > >
> > > > Any help is welcome!
> > > > Thanks.
> > > > Dietmar.
> > > >
> > > > --
> > > > Company details: http://ts.fujitsu.com/imprint.html
> > > >
> > > > _______________________________________________
> > > > Xen-devel mailing list
> > > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > > http://lists.xensource.com/xen-devel
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