Re: Populate-on-demand memory problem

[George Dunlap <George.Dunlap@eu.citrix.com>]

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@novell.com>  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@eu.citrix.com>  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@ts.fujitsu.com>  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
>>>>
>>>> _______________________________________________
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>>>> http://lists.xensource.com/xen-devel
>>>>
>>
>>
>>
>
>