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    SubjectRe: fio mmap sequential read 30% regression
    On Thu, Jul 02, 2009 at 04:01:22PM +0800, Zhang, Yanmin wrote:
    > Comapring with 2.6.30's result, fio mmap sequtial read has
    > about 30% regression on one of my stoakley machine with 1
    > JBOD (7 SAS disks) with kernel 2.6.31-rc1.
    >
    > Every disk has 2 partitions and 4 1-GB files per partition. Start
    > 10 processes per disk to do mmap read sequentinally.
    >
    > Bisect down to below patch.
    >
    > ef00e08e26dd5d84271ef706262506b82195e752 is first bad commit
    > commit ef00e08e26dd5d84271ef706262506b82195e752
    > Author: Linus Torvalds <torvalds@linux-foundation.org>
    > Date: Tue Jun 16 15:31:25 2009 -0700
    >
    > readahead: clean up and simplify the code for filemap page fault readahead
    >
    > This shouldn't really change behavior all that much, but the single rather
    > complex function with read-ahead inside a loop etc is broken up into more
    > manageable pieces.
    >
    > The behaviour is also less subtle, with the read-ahead being done up-front
    > rather than inside some subtle loop and thus avoiding the now unnecessary
    > extra state variables (ie "did_readaround" is gone).
    >
    > Fengguang: the code split in fact fixed a bug reported by Pavel Levshin:
    > the PGMAJFAULT accounting used to be bypassed when MADV_RANDOM is set, in
    > which case the original code will directly jump to no_cached_page reading.
    >
    >
    > The bisect is stable.

    Let me take care of this bug: it may well be caused by my other readahead patches.

    Thanks,
    Fengguang

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