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    SubjectRe: block cache replacement strategy?
    On Fri, Sep 10, 2010 at 06:02:48PM +0200, Johannes Stezenbach wrote:
    >
    > Linear read heuristic might be a good guess, but it would
    > be nice to hear a comment from a vm/fs expert which
    > confirms this works as intended.

    Apparently I'm unworthy to get a response from someone knowledgable :-(

    Anyway I found lmdd (from lmbench) can do random reads,
    and indeed causes the data to enter the block (page?) cache,
    replacing the previous data.


    Johannes


    zzz:~# echo 3 >/proc/sys/vm/drop_caches

    zzz:~# ./lmdd if=~js/qemu/test.img bs=1M count=1000
    1000.0000 MB in 17.7554 secs, 56.3210 MB/sec
    zzz:~# ./lmdd if=~js/qemu/test.img bs=1M count=1000
    1000.0000 MB in 0.9112 secs, 1097.4178 MB/sec

    zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat=
    norepeat on 238035072
    norepeat on 724579648
    1000.0000 MB in 21.4419 secs, 46.6376 MB/sec
    zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat=
    norepeat on 238035072
    norepeat on 724579648
    1000.0000 MB in 14.3859 secs, 69.5125 MB/sec
    zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat=
    norepeat on 238035072
    norepeat on 724579648
    1000.0000 MB in 0.8764 secs, 1141.0810 MB/sec


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