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    SubjectRe: [00/17] Large Blocksize Support V3
    On Tue, 24 Apr 2007 15:21:05 -0700 clameter@sgi.com wrote:

    > This patchset modifies the Linux kernel so that larger block sizes than
    > page size can be supported. Larger block sizes are handled by using
    > compound pages of an arbitrary order for the page cache instead of
    > single pages with order 0.

    Something I was looking for but couldn't find: suppose an application takes
    a pagefault against the third 4k page of an order-2 pagecache "page". We
    need to instantiate a pte against find_get_page(offset/4)+3. But these
    patches don't touch mm/memory.c at all and filemap_nopage() appears to
    return the zeroeth 4k page all the time in that case.

    So.. what am I missing, and how does that part work?



    Also, afaict your important requirements would be met by retaining
    PAGE_CACHE_SIZE=4k and simply ensuring that pagecache is populated by
    physically contiguous pages - so instead of allocating and adding one 4k
    page, we allocate an order-2 page and sprinkle all four page*'s into the
    radix tree in one hit. That should be fairly straightforward to do, and
    could be made indistinguishably fast from doing a single 16k page for some
    common pagecache operations (gang-insert, gang-lookup).

    The BIO and block layers will do-the-right-thing with that pagecache and
    you end up with four times more data in the SG lists, worst-case.
    -
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