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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [5874] Add virtio-balloon support
Date: Fri, 5 Dec 2008 14:14:37 +0000
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To: qemu-devel@nongnu.org
Cc: Rusty Russell <rusty@ozlabs.au.ibm.com>, Hollis Blanchard <hollisb@us.ibm.com>, kvm-devel <kvm@vger.kernel.org>

On Thursday 04 December 2008, Anthony Liguori wrote:
> Hollis Blanchard wrote:
> > On Thu, 2008-12-04 at 20:33 +0000, Anthony Liguori wrote:
> >> +static void balloon_page(void *addr, int deflate)
> >> +{
> >> +#if defined(__linux__)
> >> +    if (!kvm_enabled() || kvm_has_sync_mmu())
> >> +        madvise(addr, TARGET_PAGE_SIZE,
> >> +                deflate ? MADV_WILLNEED : MADV_DONTNEED);
> >> +#endif
> >> +}
> >
> > Hmm, I just noticed this... we need to use VIRTIO_BALLOON_PFN_SHIFT like
> > Rusty did on the kernel side.
> >
> > However, in general I'm not sure how this is supposed to work. Isn't it
> > true that madvise() is a no-op if 0 < length < getpagesize()? If so, how
> > should the guest know the chunk size needed on the host?
>
> We need to pass multiple of TARGET_PAGE_SIZE to madvise()

You mean HOST_PAGE_SIZE?

My linux manpage says that the address must be page aligned.

Paul