Re: [RFC] reduce hugetlb_instantiation_mutex usage

['David Gibson' <david@gibson.dropbear.id.au>]

On Tue, Oct 31, 2006 at 12:48:13PM +0000, Hugh Dickins wrote:
> On Tue, 31 Oct 2006, 'David Gibson' wrote:
> > On Mon, Oct 30, 2006 at 09:15:20PM -0800, Chen, Kenneth W wrote:
> > > 
> > > Instead, I'm asking how private mapping protect race between file truncation
> > > and fault? For shared mapping, it is clear to me that we are using lock_page
> > > to protect file truncate with fault.  But I don't see that protection with
> > > private mapping in current upstream kernel.
> > 
> > Oh, ok.  I can't see how it matters in the PRIVATE case, given that
> > truncate() won't, and shouldn't, truncate privately mapped pages.
> 
> Bzzt, it does and should (unless we decide to make hugetlbfs pages diverge
> from the standard for ordinary pages in this respect - could do, but that
> would require thought of its own).  

Oh, so it does.  That's not the semantic I would have guessed for
MAP_PRIVATE.

> If you've been thinking otherwise,
> that may explain why some of the accounting goes wrong.

Unlikely, given that there basically isn't any accounting for
MAP_PRIVATE pages.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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