Re: [PATCH 0/3] KVM: PPC: Book3S HV: More flexible allocator for linear memory

[Alexander Graf <agraf@suse.de>]

On 26.10.2012, at 03:17, Paul Mackerras wrote:

> On Fri, Sep 14, 2012 at 03:15:32PM +0200, Alexander Graf wrote:
>> 
>> On 14.09.2012, at 14:45, Paul Mackerras wrote:
>> 
>>> On Fri, Sep 14, 2012 at 02:13:37PM +0200, Alexander Graf wrote:
>>> 
>>>> So do you think it makes more sense to reimplement a large page allocator in KVM, as this patch set does, or improve CMA to get us really big chunks of linear memory?
>>>> 
>>>> Let's ask the Linux mm guys too :). Maybe they have an idea.
>>> 
>>> I asked the authors of CMA, and apparently it's not limited to
>>> MAX_ORDER as I feared.  It has the advantage that the memory can be
>>> used for other things such as page cache when it's not needed, but not
>>> for immovable allocations such as kmalloc.  I'm going to try it out.
>>> It will need a patch to increase the maximum alignment it allows.
>> 
>> Awesome. Thanks a lot. I'd really prefer if we can stick to generic Linux solutions rather than invent our own :).
> 
> Turns out there is a difficulty with this.  When we have a guest page
> that we want to pin in memory, and that page happens to have been
> allocated within the CMA region, we would need to migrate it out of
> the CMA region before pinning it, since otherwise it would reduce the
> amount of contiguous memory available.  But it appears that there
> isn't any way to do that.

How does this work for other users of CMA? I can't possibly believe that we only ever want a static amount of contiguous memory on the system.


Alex

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