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

[Juergen Gross <jgross@xxxxxxxx>]

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".


Juergen

> 
>> ---
>>  tools/libxl/libxl.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
>> index 0622311..f59ec42 100644
>> --- a/tools/libxl/libxl.c
>> +++ b/tools/libxl/libxl.c
>> @@ -4077,6 +4077,9 @@ int libxl_domain_setmaxmem(libxl_ctx *ctx, uint32_t 
>> domid, uint64_t max_memkb)
>>          goto out;
>>      }
>>  
>> +    libxl__xs_printf(gc, XBT_NULL, GCSPRINTF("%s/memory/static-max", 
>> dompath),
>> +                     "%"PRIu64, max_memkb);
>> +
>>      rc = 0;
>>  out:
>>      libxl_domain_config_dispose(&d_config);
>> -- 
>> 2.10.2
>>
> 


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