[Mavrick] SRU v2: Set maximum of domain visible memory to 70G

[Stefan Bader]

On 12/11/2010 05:14 PM, Tim Gardner wrote:
> On 12/10/2010 08:52 AM, Stefan Bader wrote:
>> On 12/10/2010 04:02 PM, Stefan Bader wrote:
>>> On 12/10/2010 03:52 PM, Tim Gardner wrote:
>>>> On 12/10/2010 07:10 AM, Stefan Bader wrote:
>>>>> SRU justification:
>>>>>
>>>>> Impact: The config option XEN_MAX_DOMAIN_MEMORY controls how much memory
>>>>> a Xen instance is seeing. The default for 64bit is 32GB, which is the
>>>>> reason that m2.4xlarge instances only report this amount of memory.
>>>>>
>>>>> Fix: Setting this limit to 70GB as there is a known restriction for
>>>>> t1.micro instances at about 80GB.
>>>>>
>>>>> Testcase: Booted m2.4xlarge with this set to 32GB shows 32GB of memory,
>>>>> when set to 70GB, it correctly reports 68GB. Booted a t1.micro as well
>>>>> to verify this has not caused problems there.
>>>>>
>>>>>   From c72705539ee164cdd100570c1340887f81a63d98 Mon Sep 17 00:00:00 2001
>>>>> From: Stefan Bader<stefan.bader at canonical.com>
>>>>> Date: Thu, 9 Dec 2010 17:59:36 +0100
>>>>> Subject: [PATCH] UBUNTU: Set maximum of domain visible memory to 70G
>>>>>
>>>>> BugLink: http://bugs.launchpad.net/bugs/667796
>>>>>
>>>>> Otherwise the largest instances will be stuck with 32G of memory. 70G
>>>>> was chosen as there are some known problems on small instances around
>>>>> 80GB and the largest instance is using 68GB.
>>>>>
>>>>> Signed-off-by: Stefan Bader<stefan.bader at canonical.com>
>>>>> ---
>>>>>    debian.master/config/config.common.ubuntu |    2 +-
>>>>>    1 files changed, 1 insertions(+), 1 deletions(-)
>>>>>
>>>>> diff --git a/debian.master/config/config.common.ubuntu
>>>>> b/debian.master/config/config.common.ubuntu
>>>>> index b0c486b..ed8ad01 100644
>>>>> --- a/debian.master/config/config.common.ubuntu
>>>>> +++ b/debian.master/config/config.common.ubuntu
>>>>> @@ -5014,7 +5014,7 @@ CONFIG_XEN_COMPAT_XENFS=y
>>>>>    CONFIG_XEN_DEV_EVTCHN=m
>>>>>    CONFIG_XEN_FBDEV_FRONTEND=m
>>>>>    CONFIG_XEN_KBDDEV_FRONTEND=m
>>>>> -CONFIG_XEN_MAX_DOMAIN_MEMORY=32
>>>>> +CONFIG_XEN_MAX_DOMAIN_MEMORY=70
>>>>>    CONFIG_XEN_SAVE_RESTORE=y
>>>>>    CONFIG_XEN_SCRUB_PAGES=y
>>>>>    CONFIG_XEN_SYS_HYPERVISOR=y
>>>>
>>>> Any thoughts on the impact this change will have on -generic and
>>>> -server? Perhaps we should restrict this change to the -ec2 flavour only.
>>>>
>>>> rtg
>>>
>>> As far as I understand it, this value is only used in the xen mmu code when
>>> setting up domU. The comment there says, it is in that case using a page per GB.
>>> But as we have the virtual flavour, it probably makes sense to use it.
>>>
>>> -Stefan
>>>
>>
>> Ok, so here the version 2 which only changes amd64-virtual
>>
>> -Stefan
>>
> 
> So, whats the story for Natty where CONFIG_XEN_MAX_DOMAIN_MEMORY=128 ? Won't
> that preclude booting on t1.micro ?
> 

That really was my first thought on seeing this. The longer story is, when
upstream changed this from being 8/32 as a default, they also made it
non-configurable and at the same time completely rewrote the mm code to make
their pfn-to-memory structure use a tree. So in the end, yes this is probably
the best hint to follow but no, forcing this to 70G does not resolve the problem
(I tried).

-Stefan