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    SubjectRe: [PATCH 1/4] oom: move oom_adj to signal_struct
    On Wed,  5 Aug 2009 11:29:34 +0900 (JST)
    KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

    > Hi
    >
    > > Hi, Kosaki.
    > >
    > > I am so late to invole this thread.
    > > But let me have a question.
    > >
    > > What's advantage of placing oom_adj in singal rather than task ?
    > > I mean task->oom_adj and task->signal->oom_adj ?
    > >
    > > I am sorry if you already discussed it at last threads.
    >
    > Not sorry. that's very good question.
    >
    > I'm trying to explain the detailed intention of commit 2ff05b2b4eac
    > (move oom_adj to mm_struct).
    >
    > In 2.6.30, OOM logic callflow is here.
    >
    > __out_of_memory
    > select_bad_process for each task
    > badness calculate badness of one task
    > oom_kill_process search child
    > oom_kill_task kill target task and mm shared tasks with it
    >
    > example, process-A have two thread, thread-A and thread-B and it
    > have very fat memory.
    > And, each thread have following likes oom property.
    >
    > thread-A: oom_adj = OOM_DISABLE, oom_score = 0
    > thread-B: oom_adj = 0, oom_score = very-high
    >
    > Then, select_bad_process() select thread-B, but oom_kill_task refuse
    > kill the task because thread-A have OOM_DISABLE.
    > __out_of_memory() call select_bad_process() again. but select_bad_process()
    > select the same task. It mean kernel fall in the livelock.
    >
    > The fact is, select_bad_process() must select killable task. otherwise
    > OOM logic go into livelock.
    >
    > Is this enough explanation? thanks.
    >

    Thanks for good explanation. :)

    It resulted from patch of David which moved task_struct->oom_ajd
    to mm_struct. I understood it.

    It meant oom_adj was not per-process.

    AFAIU, you want to make oom_adj per-process, again.
    And you selected the place with task->singal as per-process.

    What I have a question is that why do you select task_struct->signal
    rather than task_struct like old?

    What's benefit of using task_struct->signal ?


    --
    Kind regards,
    Minchan Kim


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