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Re: [Qemu-devel] [PATCH] kvm: align ram_size to page boundary

From: Avi Kivity
Subject: Re: [Qemu-devel] [PATCH] kvm: align ram_size to page boundary
Date: Sun, 17 Jun 2012 15:54:53 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0

On 06/17/2012 03:43 PM, Blue Swirl wrote:
> On Sun, Jun 17, 2012 at 11:51 AM, Avi Kivity <address@hidden> wrote:
>> On 06/17/2012 02:47 PM, Jan Kiszka wrote:
>>>>> I think this should rather go into generic code.
>>>> To be honest, I put this in kvm-specific code because vl.c doesn't have
>>>> TARGET_PAGE_ALIGN.  Maybe we should have machine->page_size or
>>>> machine->ram_alignment.
>>>>> What sense does it make
>>>>> to have partial pages with TCG?
>>>> Why impose an artificial restriction?
>>> Beca...
>>>> (answer: to reduce differences among various accelerators)
>>> Oh, you found the answer. :)
>> Reducing round-trips across the Internet.
>>> At least, it should be enforce for the x86 target, independent of the
>>> accelerator.
>> Yeah.  So there's machine->page_size or machine->ram_alignment.  Not
>> sure which is best.
> The boards should make sure that the amount of RAM is feasible with
> the board memory slots. It's not possible to put 256kb SIMMs to a slot
> that expects 1GB DIMMs. We can allow some flexibility there though,
> I'm not sure if the current chipsets would support very much memory if
> we followed the docs to the letter.

Right. And generally memory modules are sized a power of two, creating
the silly "mega == 1048576" movement.

> Maybe strtosz() should just enforce 1MB granularity.

strtosz() is much too general.  We could do it in vl.c without trouble.
 However, it takes away our ability to emulate a "640k should be enough
for everyone" machine.

> What about ballooning (memory hotplug?), can that reduce the memory by
> smaller amount than page size?

Ballooning removes individual pages, that has no effect on the slot size.

error compiling committee.c: too many arguments to function

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