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Date: Wed, 30 Oct 2013 16:30:35 -0200
From: Marcelo Tosatti <mtosatti@redhat.com>
Message-ID: <20131030183035.GA18378@amt.cnet>
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Subject: Re: [Qemu-devel] [patch 2/2] i386: pc: align gpa<->hpa on 1GB
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To: Gleb Natapov <gleb@redhat.com>
Cc: aarcange@redhat.com, Igor Mammedov <imammedo@redhat.com>, qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>

On Wed, Oct 30, 2013 at 10:48:13AM +0200, Gleb Natapov wrote:
> On Tue, Oct 29, 2013 at 07:21:59PM -0200, Marcelo Tosatti wrote:
> > > > Could add a warning to memory API: if memory region is larger than 1GB
> > > > and RAM is 1GB backed, and not properly aligned, warn.
> > > Perhaps it would be better do abort and ask user to fix configuration,
> > > and on hugepage allocation failure not fallback to malloc but abort and
> > > tell user amount of hugepages needed to run guest with hugepage backend.
> > 
> > You want to back your guest with 1GB hugepages. You get 1 such page at a
> > time, worst case.
> > 
> > You either 
> > 
> > 1) map the guest physical address space region (1GB sized) where
> > the hole is located with smaller page sizes, which must be 2MB, see *,
> > which requires the user to specify a different hugetlbfs mount path with
> > sufficient 2MB huge pages.
> > 
> Why not really on THP to do the work?

Because it might be the case that static hugepage assignment is desired
(no guarantees of backingwith THP).