Messages in this thread | | | Date | Thu, 8 Apr 2004 13:09:23 +1000 | From | David Gibson <> | Subject | Re: RFC: COW for hugepages |
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On Wed, Apr 07, 2004 at 07:01:26PM -0700, Andrew Morton wrote: > Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote: > > > > > > > Implementing this for ppc64 only is just wrong. Before you do this > > > I would suggest to factor out the common code in the various hugetlbpage > > > implementations and then implement it in common code. > > > > Have you actually looked at it and how huge pages are implemented > > on the various architectures ? > > > > Honestly, I don't think we have any common abstraction on things > > like hugepte's etc... actually, archs aren't even required to use > > PTEs at all. > > > > I don't see how we can make that code arch-neutral, at least not > > without a major redesign of the whole large pages mecanism. > > I don't see much in the COW code which is ppc64-specific. All the hardware > needs to do is to provide a way to make the big pages readonly. With a bit > of an abstraction for the TLB manipulation in there it should be pretty > straightforward. > > Certainly worth the attempt, no?
Yes, you have a point. However doing it in a cross-arch way will require building more of a shared abstraction about hugepage pte entries that exists currently. And that will mean making significant changes to all the archs to create that abstraction. I don't know enough about the other archs to be confident of debugging such changes, but I'll see what I can do.
That should let the actual handle_mm_fault->hugepage_cow codepath be shared. However how the hugepage ptes fit in with the rest of the pagetables varies from arch to arch - on ppc64 we're considering putting hugepages into their own entirely separate pagetables, even - so anything that actually walks the pagetables (like copy_hugetlb_page_range()) will still have to be arch-specific.
-- David Gibson | For every complex problem there is a david AT gibson.dropbear.id.au | solution which is simple, neat and | wrong. http://www.ozlabs.org/people/dgibson - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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