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SubjectRe: [patch -mm v2] mm: introduce oom_adj_child
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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".

Thanks,
-Kame

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