[Xen-devel] Re: Why p2m allocation is from hap or shadow preallocated memory?

[Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>]

Hi Xin,

At 15:54 +0800 on 07 Aug (1186502042), Li, Xin B wrote:
> And can we make p2m memory allocation from domain heap directly?

We shouldn't pull from the domheap directly because it's not accounted
for.  This was a problem with the old shadow code, which just kept
pulling un-owned pages from the domheap until it (or sometimes Xen) fell
over.  The shadow memory allocation is explicitly separate and can be
accounted to the guest that's using it and tracked by the tools.

There are still a number of places, particularly in the HVM platform
code, where unaccounted domheap memory is used for per-domain or
per-vcpu structures, but at least they're usually small (~1 page) and
static (no need to allocate more at run-time and have domains blow up
unpredictably, and reasonable confidence that domheap won't drain away
when we're not looking).

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, XenSource UK Limited
Registered office c/o EC2Y 5EB, UK; company number 05334508

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