linux-kernel - Re: [PATCH, RESEND] introduce get_mm_hiwater_xxx(), fix taskstats->hiwater

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Message-ID: <20081213034850.GE4365@balbir.in.ibm.com>
Date:	Sat, 13 Dec 2008 09:18:50 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hugh@...itas.com>, Jay Lan <jlan@....com>,
	Jiri Pirko <jpirko@...hat.com>, Jonathan Lim <jlim@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RESEND] introduce get_mm_hiwater_xxx(), fix
	taskstats->hiwater_xxx accounting

* KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [2008-12-13 11:34:53]:

> > (changes: update the changelog/comments)
> >
> > xacct_add_tsk() relies on do_exit()->update_hiwater_xxx() and uses
> > mm->hiwater_xxx directly, this leads to 2 problems:
> >
> >        - taskstats_user_cmd() can call fill_pid()->xacct_add_tsk()
> >          at any moment before the task exits, so we should check the
> >          current values of rss/vm anyway.
> >
> >        - do_exit()->update_hiwater_xxx() calls are racy. An exiting
> >          thread can be preempted right before mm->hiwater_xxx = new_val,
> >          and another thread can use A_LOT of memory and exit in between.
> >          When the first thread resumes it can be the last thread in the
> >          thread group, in that case we report the wrong hiwater_xxx
> >          values which do not take A_LOT into account.
> >
> > Introduce get_mm_hiwater_rss() and get_mm_hiwater_vm() helpers and
> > change xacct_add_tsk() to use them. The first helper will also be
> > used by rusage->ru_maxrss accounting.
> >
> > Kill do_exit()->update_hiwater_xxx() calls. Unless we are going to
> > decrease rss/vm there is no point to update mm->hiwater_xxx, and
> > nobody can look at this mm_struct when exit_mmap() actually unmaps
> > the memory.
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> 
> Thanks! looks good to me.
>    Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

Me too, I am acking it, but you already have all the acks you need :)

Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com>

-- 
	Balbir
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