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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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