Re: [Qemu-devel] [PATCH QEMU] transparent hugepage support

[Avi Kivity]

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.