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    SubjectRe: [00/17] Large Blocksize Support V3
    Christoph Lameter wrote:
    > On Fri, 27 Apr 2007, Nick Piggin wrote:
    >
    >
    >>For the TLB issue, higher order pagecache doesn't help. If distros
    >>ship with a 4K page size on powerpc, and use some larger pages in
    >>the pagecache, some people are still going to get angry because
    >>they wanted to use 64K pages... But I agree 64K pages is too big
    >>for most things anyway, and 16 would be better as a default (which
    >>hopefully x86-64 will get one day).
    >
    >
    > Powerpc supports multiple pagesizes. Maybe we could make mmap use those
    > page sizes some day if we had a variable order page cache. Your stands on
    > the issue means that powerpc will be forever crippled and not be able to
    > use its full potential.

    Linus's favourite jokes about powerpc mmu being crippled forever, aside ;)

    This seems like just speculation. I would not be against something which,
    without, would "cripple" some relevant hardware, but you are just handwaving
    at this point. And you are still ignoring the alternatives.


    >>Anyway, for io performance, there are alternatives, dispite what
    >>some people seem to be saying. We can submit larger sglists to the
    >>device for larger ios, which Jens is looking at (which could help
    >>all types of workloads, not just those with sequential large file
    >>IO).
    >
    >
    > Right this could help but it is not addressing the basic requirement for
    > devices that need large contiguuos chunks of memory for I/O.

    Did you read the last paragraph? Or anything Andrew's been writing?

    "After that, I'd find it amusing if HBAs worth thousands of $ have
    trouble looking up sglists at the relatively glacial pace that IO
    requires, and/or can't spare a few more K for reasonable sglist
    sizes, but if that is really the case, then we could use iommus
    and/or just attempt to put physically contiguous pages in pagecache,
    rather than require it."

    --
    SUSE Labs, Novell Inc.
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