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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH QEMU] transparent hugepage support
Date: Thu, 11 Mar 2010 16:28:04 +0000
References: <20100311151427.GE5677@random.random> <4B9911B0.5000302@redhat.com>
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To: qemu-devel@nongnu.org
Cc: Andrea Arcangeli <aarcange@redhat.com>, Avi Kivity <avi@redhat.com>

> > +		/*
> > +		 * Align on HPAGE_SIZE so "(gfn ^ pfn)&
> > +		 * (HPAGE_SIZE-1) == 0" to allow KVM to take advantage
> > +		 * of hugepages with NPT/EPT.
> > +		 */
> > +		new_block->host = qemu_memalign(1<<  TARGET_HPAGE_BITS, size);

This should not be target dependent. i.e. it should be the host page size.

> That is a little wasteful.  How about a hint to mmap() requesting proper
> alignment (MAP_HPAGE_ALIGN)?

I'd kinda hope that we wouldn't need to. i.e. the host kernel is smart enough 
to automatically align large allocations anyway.

This is probably a useful optimization regardless of KVM.

Paul