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    SubjectRe: OOM notifications
    Andrew Morton wrote:
    > On Thu, 18 Oct 2007 16:15:31 -0400
    > Marcelo Tosatti <> wrote:
    >> Hi,
    >> AIX contains the SIGDANGER signal to notify applications to free up some
    >> unused cached memory:
    >> There have been a few discussions on implementing such an idea on Linux,
    >> but nothing concrete has been achieved.
    >> On the kernel side Rik suggested two notification points: "about to
    >> swap" (for desktop scenarios) and "about to OOM" (for embedded-like
    >> scenarios).
    >> With that assumption in mind it would be necessary to either have two
    >> special devices for notification, or somehow indicate both events
    >> through the same file descriptor.
    >> Comments are more than welcome.
    > Martin was talking about some mad scheme wherin you'd create a bunch of
    > pseudo files (say, /proc/foo/0, /proc/foo/1, ..., /proc/foo/9) and each one
    > would become "ready" when the MM scanning priority reaches 10%, 20%, ...
    > 100%.
    > Obviously there would need to be a lot of abstraction to unhook a permanent
    > userspace feature from a transient kernel implementation, but the basic
    > idea is that a process which wants to know when the VM is getting into the
    > orange zone would select() on the file "7" and a process which wants to
    > know when the VM is getting into the red zone would select on file "9".
    > It get more complicated with NUMA memory nodes and cgroup memory
    > controllers.

    We ended up not doing that, but making a scanner that saw what
    percentage of the LRU was touched in the last n seconds, and
    printing that to userspace to deal with.

    Turns out priority is a horrible metric to use for this - it
    stays at default for ages, then falls off a cliff far too
    quickly to react to.

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      Last update: 2007-10-26 23:09    [W:0.021 / U:48.836 seconds]
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