[Xen-devel] Re: Hugepage support to tmem.

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

Hi, 

At 01:51 +0100 on 25 Oct (1287971515), Dan Magenheimer wrote:
> > I think that in design consideration we need to solve this problem of
> > splitting.
> > 
> > According to code such splitting is done in HAP, so what exactly
> > happens in shadow mode?
> 
> I think Tim Deegan is much more of an expert in this area than
> I am.  I have cc'ed him.

Shadow mode always uses 4k mappings for everything.  It should be
possible to update it to use 2M mappings when the underlying memory is
both contiguous and all the same type, but it would take a bit of
cunning to do it without making refcounting very expensive.

HAP uses 2M mappings when it can - even the PoD code tries not to
fragment into 4k mappings.  But if you're running PoD you're also using
balloon drivers, and they always operate in 4K pages.  AFAIK, all
existing balloon drivers will tend to fragment memory.

Cheers,

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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