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    SubjectRe: [parisc-linux] Re: Problems with kernel mmap (failing tst-mmap-eofsync in glibc on parisc)
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    On Sun, 2003-08-24 at 00:23, David S. Miller wrote:
    > This is what I'm asking of you, to find cases in real life,
    > not some contrived example, where your optimization helps
    > appreciably.

    Oh, OK, that's easy...it's what the glibc test was designed for.

    In glibc, for each file you fopen as a mapped file, you seem to get a
    separate mmapping of the file (this actually looks wrong to me...it
    seems glibc should have only one mapping per file which all the file
    objects share, but anyway). That means we get one entry in one of the
    i_mmaps lists for each of the opens. Since these are files, the chances
    are they'll be read and written which will generate lots of dcache
    flushes. This case would kill us if we had to flush every entry in
    i_mmap.

    Right at the moment, you have to specifically request that the file be
    mmapped by specifying the "m" modifier, but glibc seems to be migrating
    to this being the default one day...that's what I want to be ready for.

    Besides the optimisation adds no overhead and compromises nothing, so
    its worth doing regardless.

    James


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