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    SubjectRe: [patch 00/14] Page cache cleanup in anticipation of Large Blocksize support
    On Thu, 14 Jun 2007 19:04:27 -0700 (PDT) Christoph Lameter <clameter@sgi.com> wrote:

    > > > Of course there is. The seeks are reduced since there are an factor
    > > > of 16 less metadata blocks. fsck does not read files. It just reads
    > > > metadata structures. And the larger contiguous areas the faster.
    > >
    > > Some metadata is contiguous: inode tables, some directories (if they got
    > > lucky), bitmap tables. But fsck surely reads them in a single swoop
    > > anyway, so there's no gain there.
    >
    > The metadata needs to refer to 1/16th of the earlier pages that need to be
    > tracked. metadata is shrunk significantly.

    Only if the filesystems are altered to use larger blocksizes and if the
    operator then chooses to use that feature. Then they suck for small-sized
    (and even medium-sized) files.

    So you're still talking about corner cases: specialised applications which
    require careful setup and administrator intervention.

    What can we do to optimise the common case?

    > > Other metadata (indirect blocks) are 100% discontiguous, and reading those
    > > with a 64k IO into 64k of memory is completely dumb.
    >
    > The effect of a larger page size is that the filesystem will
    > place more meta data into a single page instead of spreading it out.
    > Reading a mass of meta data with a 64k read is an intelligent choice to
    > make in particular if there is a large series of such reads.

    Again: requires larger blocksize: specialised, uninteresting for what will
    remain the common case: 4k blocksize.

    The alleged fsck benefit is also unrelated to variable PAGE_CACHE_SIZE.
    It's a feature of larger (unweildy?) blocksize, and xfs already has that
    working (doesn't it?)

    There may be some benefits to some future version of ext4.
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