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    SubjectRe: [00/17] Large Blocksize Support V3
    On Fri, Apr 27 2007, Nick Piggin wrote:
    > Why do we limit drivers to 128 sg entries?

    No particular reason, except than to avoid 2^bigger order allocations.
    2MiB requests would require 3 contig pages to setup the sg list, which
    is (probably) a little troublesome especially since it's sometimes
    atomically allocated.

    Larger pages are by no means a prerequisite to getting larger requests,
    assuming your hardware can handle the bigger sglist. There are other
    ways of doing that, I've contemplated doing chained sglists and adding
    sg_for_each_segment() macros for iterating these things. Drivers that
    want larger sglists would then be required to update their sg mapping
    loop to use the provided macros. It wouldn't be too hard.

    --
    Jens Axboe

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