Re: [PATCH 4/4] Hugetlb: Copy on Write support

From: David Gibson (david_at_gibson.dropbear.id.au)
Date: 11/10/05

  • Next message: William Lee Irwin III: "Re: [PATCH 4/4] Hugetlb: Copy on Write support" 
    Date:	Thu, 10 Nov 2005 11:49:07 +1100
To: William Lee Irwin III <wli@holomorphy.com>

    On Wed, Nov 09, 2005 at 04:15:34PM -0800, William Lee Irwin wrote:
    > On Wed, Nov 09, 2005 at 05:39:55PM -0600, Adam Litke wrote:
    > > Hugetlb: Copy on Write support
    > > Implement copy-on-write support for hugetlb mappings so MAP_PRIVATE can be
    > > supported. This helps us to safely use hugetlb pages in many more
    > > applications. The patch makes the following changes. If needed, I also have
    > > it broken out according to the following paragraphs.
    > > 1. Add a pair of functions to set/clear write access on huge ptes. The
    > > writable check in make_huge_pte is moved out to the caller for use by COW
    > > later.
    > > 2. Hugetlb copy-on-write requires special case handling in the following
    > > situations:
    > > - copy_hugetlb_page_range() - Copied pages must be write protected so a COW
    > > fault will be triggered (if necessary) if those pages are written to.
    > > - find_or_alloc_huge_page() - Only MAP_SHARED pages are added to the page
    > > cache. MAP_PRIVATE pages still need to be locked however.
    > > 3. Provide hugetlb_cow() and calls from hugetlb_fault() and hugetlb_no_page()
    > > which handles the COW fault by making the actual copy.
    > > 4. Remove the check in hugetlbfs_file_map() so that MAP_PRIVATE mmaps will be
    > > allowed. Make MAP_HUGETLB exempt from the depricated VM_RESERVED mapping
    > > check.
    >
    > Did you do the audit of pte protection bits I asked about? If not, I'll
    > dredge them up and check to make sure.

    I still don't know what you're talking about here - you never
    responded to my mail asking for clarification. The hugepage code
    already relies on pte_mkwrite() and pte_wrprotect() working correctly,
    I don't see that COW makes any difference. 

    -- 
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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  • Next message: William Lee Irwin III: "Re: [PATCH 4/4] Hugetlb: Copy on Write support"

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