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    SubjectRe: [PATCH 12/33] readahead: min/max sizes
    On Thu, May 25, 2006 at 02:50:59PM +1000, Nick Piggin wrote:
    > Wu Fengguang wrote:
    > >- Enlarge VM_MAX_READAHEAD to 1024 if new read-ahead code is compiled in.
    > > This value is no longer tightly coupled with the thrashing problem,
    > > therefore constrained by it. The adaptive read-ahead logic merely takes
    > > it as an upper bound, and will not stick to it under memory pressure.
    > >
    > I guess this size enlargement is one of the main reasons your
    > patchset improves performance in some cases.

    Sure, I started the patch to fulfill the 1M _default_ size dream ;-)
    The majority users will never enjoy the performance improvement if
    ever we stick to 128k default size. And it won't be possible for the
    current readahead logic, since it lacks basic thrashing protection

    > There is currently some sort of thrashing protection in there.
    > Obviously you've found it to be unable to cope with some situations
    > and introduced a lot of really fancy stuff to fix it. Are these just
    > academic access patterns, or do you have real test cases that
    > demonstrate this failure (ie. can we try to incrementally improve
    > the current logic as well as work towards merging your readahead
    > rewrite?)

    But to be serious, in the progress I realized that it's much more
    beyond the max readahead size. The fancy features are more coming out
    of _real_ needs than to fulfill academic goals. I've seen real world
    improvements from desktop/file server/backup server/database users
    for most of the implemented features.

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      Last update: 2006-05-25 14:15    [W:0.022 / U:8.792 seconds]
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