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    SubjectRe: [PATCH 00/23] Adaptive read-ahead V11
    On Sun, Mar 19, 2006 at 10:53:46AM -0500, Jon Smirl wrote:
    > In another thread someone made a mention that this problem may have
    > something to do with the pools of memory being used for sendfile. The
    > readahead from sendfile is going into a moderately sized pool. When
    > you get 100 of them going at once the other threads flush the
    > readahead data out of the pool before it can be used and thus trigger
    > the thrashing seek storm. Is this true, that sendfile data is read
    > ahead into a fixed sized pool? If so, the readahead algorithms would

    The pages are kept in a cache pool which is made of all the free memory.
    E.g. the following command shows a system with 331M cache pool:

    % free -m
    total used free shared buffers cached
    Mem: 488 482 5 0 7 331
    -/+ buffers/cache: 142 345
    Swap: 127 0 127

    That would be more than enough for the stock read-ahead to handle 100
    concurrent readers.

    > need to reduce the sendfile window sizes to stop the pool from
    > thrashing.

    Sure, it is the desired behavior. This patch provides exactly this feature :)

    Cheers,
    Wu
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