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    SubjectRe: [RFC] kernel facilities for cache prefetching
    On Tue, May 02, 2006 at 10:09:36AM +0200, Jens Axboe wrote:
    > Your patch isn't exactly pretty, but that is fixable. I'm more
    > interested in how you'd control that sanely.

    I have a quick and dirty hack called BootCache (only afterwards did I notice
    that Apple used the same name) that snoops all the read requests during
    startup and uses that to populate a file which gets read in to populate
    the cache on subsequent boots. The results are impressive: eliminating
    the seeks (since the file is contiguous) results in 15s (out of the 45s
    from init starting to the login prompt) reduction in boot time on ext3.

    Prefetch without reordering isn't particularly effective, as the cost of
    the seeks to read in the inodes and file data tend to block critical path
    io in the startup scripts.

    I hope to release the code sometime soon and rework it to be a better fit
    for merging with the kernel -- it should be possible to use the block io
    tracing facility to log the blocks required and then feed that back into
    the filesystem to reallocate blocks in the filesystem. That would eliminate
    the messy part of bootcache that has to snoop block writes to maintain the
    cache. This is all part of what I'm aiming to present at OLS.

    "Time is of no importance, Mr. President, only life is important."
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