Re: [Xen-devel] [PATCH] tools/libxl: modify static-max in xenstore when setting maxmem

[Juergen Gross <jgross@xxxxxxxx>]

On 19/01/17 13:51, Juergen Gross wrote:
> On 19/01/17 12:51, Wei Liu wrote:
>> On Wed, Jan 18, 2017 at 07:25:57PM +0100, Juergen Gross wrote:
>>> xl mem-max is setting the hypervisor memory limit of a domain, but not
>>> the memory/static-max value in Xenstore. This prohibits setting the
>>> memory size above the old maximum size.
>>>
>>> Set the new maximum value in Xenstore.
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>
>> This looks sensible. But memory accounting is a thorny area.
>>
>> Could you try to do local migration test for both PV and HVM guests with
>> this patch applied (with or w/out changing maxmem)?
> 
> PV: works (both with or without maxmem changed)
> HVM: works only with unchanged maxmem
> 
> HVM with changed maxmem will trigger an assertion in qemu for the
> incoming domain:
> 
> xen_ram_alloc: do not alloc 37c00000 bytes of ram at 0 when runstate is
> INMIGRATE
> xen_ram_alloc: do not alloc 800000 bytes of ram at 37c00000 when
> runstate is INMIGRATE
> qemu-system-i386:
> /home/gross/xen/tools/qemu-xen-dir/include/exec/ram_addr.h:49:
> ramblock_ptr: Assertion `offset_in_ramblock(block, offset)' failed.
> 
> Without my patch this is working, but the migrated domain has the old
> maxmem in hypervisor data as can be seen via "xl debug-keys q".

This is all very strange:

Starting a HVM domain with maxmem=1124 and memory=1024 will place the
correct size in Xenstore, but max_pages in the hypervisor is showing
1025 MB only.

Can anybody tell me how the sizes should be set?


Juergen

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