Re: Design question for PV superpage support

[Mick Jordan <Mick.Jordan@sun.com>]

[-- Attachment #1.1: Type: text/plain, Size: 1602 bytes --]

On 03/02/09 09:06, Keir Fraser wrote:
> On 02/03/2009 16:43, "Mick Jordan" <Mick.Jordan@sun.com> wrote:
>
>   
>> On 03/02/09 05:54, Dave McCracken wrote:
>>     
>>> The solution I am working on for how to support Linux hugepages (Xen
>>> superpages) involves creating domains made up entirely of superpages.  I can
>>> create a working domain with superpages and am in the process of supporting
>>> it in save/restore.
>>>   
>>>       
>> This wouldn't work too well for me in the case of thread stacks because
>> we need to map out parts of the stack and, although we want large
>> virtual stacks, we don't want do dedicate that much physical memory. Is
>> it really difficult to support mixed pages sizes in the general case,
>> e.g., save/restore etc.?
>>     
>
> You can still make 4kB mappings of subsections of 2MB physical extents. And
> the guest kernel will still be able to allocate subsections of 2MB physical
> extents for various uses. Isn't that all you need for e.g., this thread
> stack situation?
>
>   
Yes, that would work. Assuming it doesn't cause problems in other ways, 
e.g. save/restore, given that this re-introduces mixed mappings. I'd 
appreciate someone explaining the problems for save/restore with the 
earlier patch that simply allowed 2MB pages in PTEs.
> Presumably Dave McCracken will be implementing a 'best effort' mode for
> domains where we try to allocate superpages but we get by at reduced
> performance if we have to allocate some discontiguous extents due to lack of
> contiguous available memory. That would be reasonably sensible.
>
>   
Indeed.
Mick


[-- Attachment #1.2: Type: text/html, Size: 2347 bytes --]

[-- Attachment #2: Type: text/plain, Size: 138 bytes --]

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel