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    SubjectRe: [PATCH] x86: Construct 32 bit boot time page tables in native format.
    Ian Campbell wrote:
    > On Sun, 2008-01-20 at 20:30 +0200, Mika Penttilä wrote:
    >>>
    >> You have dropped the requirement to map all of low memory (the boot
    >> allocator is used for instance to construct physical mem mapping).
    >> Either you should fix your INIT_MAP_BEYOND_END or make a big comment
    >> telling us why it isn't necessary anymore to map low mem.
    >
    > I think you are right. The patch ensures that all the initial page
    > tables themselves have mappings but won't map the additional pages
    > needed for mapping the rest of lowmem.
    >
    > However, I think it is no longer necessary to map a whole new 4G worth
    > of page table pages because the code in kernel_physical_mapping_init now
    > extends the initial mappings rather than replacing them (see changes to
    > native_pagetable_setup_start). So now we only need to map 4G worth of
    > page tables including the initial page tables. That means we only need
    > to map a fixed set of extra pages rather than the sliding limit
    > currently used in the patch.
    >

    We still need to be able to construct those page tables, which is what
    that stuff is about...


    > I'm not convinced by the additional 16MB for CONFIG_DEBUG_PAGEALLOC --
    > we map enough pages for page tables for 4G of lowmem -- adding space for
    > an extra 16M seems pointless.

    If so, adjusting the limit should be a separate patch.

    Either way, I'm increasingly thinking that setting up the initial page
    tables via an assembly loop instead of worrying about the C accessors is
    actually cleaner (I prototyped it yesterday, although I still need the
    rest of the machinery.)


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