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    SubjectRe: [patch -mm v2] mm: introduce oom_adj_child
    David Rientjes wrote:

    >> > It livelocks if a thread is chosen and passed to oom_kill_task() while
    >> > another per-thread oom_adj value is OOM_DISABLE for a thread sharing
    >> the
    >> > same memory.
    >> >
    >> I say "why don't modify buggy selection logic?"
    >> Why we have to scan all threads ?
    >> As fs/proc/readdir does, you can scan only "process group leader".
    >> per-thread scan itself is buggy because now we have per-process
    >> effective-oom-adj.
    > Without my patches to change oom_adj from task_struct to mm_struct, you'd
    > need to scan all tasks and not just the tgids because their oom_adj values
    > can differ amongst threads in the same thread group. So while it may now
    > be possible to shorten the scan as a result of my approach, it isn't a
    > solution itself to the problem.

    Did I said "revert your patch in -rc" even once ?
    livelock-avoidance itself is good work, thank you.
    All my suggestion is based on your patch already in rc4.
    Summarizing I think now .....
    - rename mm->oom_adj as mm->effective_oom_adj
    - re-add per-thread oom_adj
    - update mm->effective_oom_adj based on per-thread oom_adj
    - if necessary, plz add read-only /proc/pid/effective_oom_adj file.
    or show 2 values in /proc/pid/oom_adj
    - rewrite documentation about oom_score.
    " it's calclulated from _process's_ memory usage and oom_adj of
    all threads which shares a memor context".
    This behavior is not changed from old implemtation, anyway.
    - If necessary, rewrite oom_kill itself to scan only thread group
    leader. It's a way to go regardless of vfork problem.

    >> > How else do you propose the oom killer use oom_adj values on a
    >> per-thread
    >> > basis without considering other threads sharing the same memory?
    >> As I wrote.
    >> per-process(signal struct) or per-thread oom_adj and add
    >> mm->effecitve_oom_adj
    >> task scanning isn't necessary to do per-thread scan and you can scan
    >> only process-group-leader. What's bad ?
    >> If oom_score is problem, plz fix it to show effective_oom_score.
    > When only using (and showing) mm->effective_oom_adj for a task, userspace
    > will not be able to adjust /proc/pid/oom_score with /proc/pid/oom_adj
    > as Documentation/filesystems/proc.txt says you can for a thread unless it
    > exceeds effective_oom_adj.>

    Is it different from old behavior ?
    I think documentation is wrong. It should say "you should think of
    multi-thread effect to oom_adj/oom_score".


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