Re: swapping and the value of /proc/sys/vm/swappiness

From: William Lee Irwin III (wli_at_holomorphy.com)
Date: 09/07/04

  • Next message: Con Kolivas: "Re: sched_setaffinity(), RT priorities and migration thread usage at 30%" 
    Date:	Mon, 6 Sep 2004 15:48:30 -0700
To: Ray Bryant <raybry@sgi.com>

    On Mon, Sep 06, 2004 at 02:11:29PM -0500, Ray Bryant wrote:
    > What is unexpected is that the amount of swap space used at a particular
    > swappiness setting varies dramatically with the kernel version being
    > tested, in spite of the fact that the basic swap_tendency calculation in
    > refile_ianctive_zone() is unchanged. (Other, subtle changes in the vm as a
    > whole and this routine in particular clearly effect the impact of that
    > computation.)
    > For example, at a swappiness value of 0, Kernel 2.6.5 swapped out 0 bytes,
    > whereas Kernel 2.6.9-rc1-mm3 swapped out 10 GB. Similarly, most kernels
    > have a significant change in behavior for swappiness values near 100, but
    > for SLES9 the change point occurs at swappness=60.
    > A scan of the change logs for swappiness related changes shows nothing that
    > might explain these changes. My question is: "Is this change in behavior
    > deliberate, or just a side effect of other changes that were made in the
    > vm?" and "What kind of swappiness behavior might I expect to find in future
    > kernels?".

    IIRC no deliberate /proc/sys/vm/swappiness semantic changes were merged.
    The policy tweakers have something to answer for here unless some stats
    they rely upon have since been flubbed. Logging periodic snapshots of
    /proc/vmstat for these benchmarks may be helpful to implicate specific
    statistics' bungling or rule out statistic miscalculation as causes.

    -- wli
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  • Next message: Con Kolivas: "Re: sched_setaffinity(), RT priorities and migration thread usage at 30%"

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