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Date: Sat, 13 Mar 2010 10:28:32 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH QEMU] transparent hugepage support
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To: Andrea Arcangeli <aarcange@redhat.com>
Cc: qemu-devel@nongnu.org

On 03/11/2010 06:05 PM, Andrea Arcangeli wrote:
> On Thu, Mar 11, 2010 at 05:52:16PM +0200, Avi Kivity wrote:
>    
>> That is a little wasteful.  How about a hint to mmap() requesting proper
>> alignment (MAP_HPAGE_ALIGN)?
>>      
> So you suggest adding a new kernel feature to mmap? Not sure if it's
> worth it, considering it'd also increase the number of vmas because it
> will have to leave an hole. Wasting 2M-4k of virtual memory is likely
> cheaper than having 1 more vma in the rbtree for every page fault. So
> I think it's better to just malloc and adjust ourselfs on the next
> offset which is done in userland by qemu_memalign I think.
>
>    

Won't we get a new vma anyway due to the madvise() call later?

But I agree it isn't worth it.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.