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    SubjectRe: User space out of memory approach
    On Mon, 10 Jan 2005 17:39:53 -0200, Marcelo Tosatti
    <marcelo.tosatti@cyclades.com> wrote:
    > On Mon, Jan 10, 2005 at 05:20:13PM -0200, Marcelo Tosatti wrote:
    > > On Mon, Jan 10, 2005 at 05:43:23PM -0400, Mauricio Lin wrote:
    > > > Hi all,
    > > >
    > > > We have done a comparison between the kernel version and user space
    > > > version and apparently the behavior is similar. You can also get this
    > > > patch and module to test it and compare with kernel OOM Killer. Here
    > > > goes a patch and a module that moves the kernel space OOM Killer
    > > > algorithm to user space. Let us know about your ideas.
    > >
    > > No comments on the code itself - It is interesting to have certain pids "not selectable" by
    > > the OOM killer. Patches which have similar funcionality have been floating around.
    > >
    > > The userspace OOM killer is dangerous though. You have to guarantee that allocations
    > > will NOT happen until the OOM killer is executed and the killed process is dead and
    > > has its pages freed - allocations under OOM can cause deadlocks.
    > >
    > > "OOM-killer-in-userspace" is unreliable, not sure if its worth the effort making
    > > it reliable (mlock it, flagged as PF_MEMALLOC, etc).
    >
    > Actually its only unreliable if its called from OOM time.
    >
    > The case here is you have a daemon which periodically writes
    > to /proc/oom ?
    Yes, let me explain the idea.
    When the memory consumption reaches a percentage of usage, as 98% or
    something like that, we call this as red zone. So when red zone is
    reached, the ranking algorithm is started to select which processes
    could be killed whe out of memory happens. If the memory comsumption
    is less than this percentage (not in red zone), the ranking algorithm
    is not executed. So we have a loop the check the memory comsumption
    all the time and if the red zone is reached, the ranking algorithm is
    started before the system get the out of memory state.

    BR,

    Mauricio Lin.
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