linux-kernel - Re: [patch -mm v2] mm: introduce oom_adj

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Message-ID: <7f54310137837631f2526d4e335287fc.squirrel@webmail-b.css.fujitsu.com>
Date:	Fri, 31 Jul 2009 19:49:02 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	"David Rientjes" <rientjes@...gle.com>
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Rik van Riel" <riel@...hat.com>,
	"Paul Menage" <menage@...gle.com>,
	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch -mm v2] mm: introduce oom_adj_child

David Rientjes wrote:
> On Fri, 31 Jul 2009, KAMEZAWA Hiroyuki wrote:
>
>> > > Simply, reset_oom_adj_at_new_mm_context or some.
>> > >
>> >
>> > I think it's preferred to keep the name relatively short which is an
>> > unfortuante requirement in this case.  I also prefer to start the name
>> > with "oom_adj" so it appears alongside /proc/pid/oom_adj when listed
>> > alphabetically.
>> >
>> But misleading name is bad.
>>
>
> Can you help think of any names that start with oom_adj_* and are
> relatively short?  I'd happily ack it.
>
There have been traditional name "effective" as uid and euid.

 then,  per thread oom_adj as oom_adj
        per proc   oom_adj as effective_oom_adj

is an natural way as Unix, I think.



>> Why don't you think select_bad_process()-> oom_kill_task()
>> implementation is bad ?
>
> 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.


>> IMHO, it's bad manner to fix an os-implementation problem by adding
>> _new_ user
>> interface which is hard to understand.
>>
>
> 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.

If you can wait until the end of August, plz wait. I'll do some.

Thanks,
-Kame

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