linux-kernel - Re: [patch 7/7 -mm] oom: remove unnecessary code and cleanup

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Message-Id: <20100215173046.72A4.A69D9226@jp.fujitsu.com>
Date:	Mon, 15 Feb 2010 17:31:38 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 7/7 -mm] oom: remove unnecessary code and cleanup

> On Fri, 12 Feb 2010, KAMEZAWA Hiroyuki wrote:
> 
> > > Remove the redundancy in __oom_kill_task() since:
> > > 
> > >  - init can never be passed to this function: it will never be PF_EXITING
> > >    or selectable from select_bad_process(), and
> > > 
> > >  - it will never be passed a task from oom_kill_task() without an ->mm
> > >    and we're unconcerned about detachment from exiting tasks, there's no
> > >    reason to protect them against SIGKILL or access to memory reserves.
> > > 
> > > Also moves the kernel log message to a higher level since the verbosity
> > > is not always emitted here; we need not print an error message if an
> > > exiting task is given a longer timeslice.
> > > 
> > > Signed-off-by: David Rientjes <rientjes@...gle.com>
> > 
> > If you say "never", it's better to add BUG_ON() rather than 
> > if (!p->mm)...
> > 
> 
> As the description says, oom_kill_task() never passes __oom_kill_task() a 
> task, p, where !p->mm, but it doesn't imply that p cannot detach its ->mm 
> before __oom_kill_task() gets a chance to run.  The point is that we don't 
> really care about giving it access to memory reserves anymore since it's 
> exiting and won't be allocating anything.  Warning about that scenario is 
> unnecessary and would simply spam the kernel log, a recall to the oom 
> killer would no longer select this task in case the oom condition persists 
> anyway.

I agree this description is correct and this code is unnecessary.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>


> 
> > But yes, this patch seesm to remove unnecessary codes.
> > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > 
> 
> Thanks!
> 
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