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    SubjectRe: [PATCH -v2 -mm] add extra free kbytes tunable
    On Thu, 1 Sep 2011, Andrew Morton wrote:

    > > Add a userspace visible knob
    > argh. Fear and hostility at new knobs which need to be maintained for
    > ever, even if the underlying implementation changes.

    Do we really need to maintain tunables that lose their purpose either
    because the implementation changes or is patched to fix the issue that the
    tunable was intended to address without requiring it?

    Are there really userspace tools written to not be able to handle -ENOENT
    when one of these gets removed?

    > > It may also be useful to reduce the memory use of virtual
    > > machines (temporarily?), in a way that does not cause memory
    > > fragmentation like ballooning does.
    > Maybe. You need to alter the setting, then somehow persuade all the
    > targeted kswapd's to start running, then somehow determine that they've
    > done their thing, then unalter the /proc setting. Not the best API
    > we've ever designed ;)

    And, unfortunately, this could have negative effects if using cpusets
    and/or mempolicies since this is global across all zones such that jobs
    that do not require such "extra" memory would be unfairly penalized with
    work incurred by additional reclaim they don't need. And if the job is
    constrained to a memory cgroup, there's no guarantee it will reclaim back
    to these altered watermarks.

     \ /
      Last update: 2011-09-02 00:11    [W:0.021 / U:37.052 seconds]
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