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    SubjectRe: [PATCH] MM: implement MADV_FREE lazy freeing of anonymous memory
    Nick Piggin wrote:
    > Rik van Riel wrote:
    >> With lazy freeing of anonymous pages through MADV_FREE, performance of
    >> the MySQL sysbench workload more than doubles on my quad-core system.
    >
    > OK, I've run some tests on a 16 core Opteron system, both sysbench with
    > MySQL 5.33 (set up as described in the freebsd vs linux page), and with
    > ebizzy.
    >
    > What I found is that, on this system, MADV_FREE performance improvement
    > was in the noise when you look at it on top of the MADV_DONTNEED glibc
    > and down_read(mmap_sem) patch in sysbench.

    It turns out that setting the pte accessed bit in hardware
    can apparently take a few thousand CPU cycles - 3000 cycles
    is the number I've heard for one CPU family.

    This is a similar number of cycles as is needed to zero out
    a page. Giving a cache hot page to userspace could cancel
    out the rest of the cost of the page fault handling.

    Lets stick with the simpler MADV_DONTNEED code for now and
    save the page flag for something else...

    --
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    the best in the world, and those who believe it already is. Each group
    calls the other unpatriotic.
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