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

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Message-ID: <20081206103904.GC24782@balbir.in.ibm.com>
Date:	Sat, 6 Dec 2008 16:09:04 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Jay Lan <jlan@....com>, Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Pirko <jpirko@...hat.com>, linux-kernel@...r.kernel.org,
	Jonathan Lim <jlim@....com>
Subject: Re: [PATCH] introduce get_mm_hiwater_xxx(), fix
	taskstats->hiwater_xxx accounting

* Hugh Dickins <hugh@...itas.com> [2008-12-06 09:56:19]:

> On Sat, 6 Dec 2008, Balbir Singh wrote:
> > 
> > Yes, true and getdelays can display all the exported information.
> > 
> > The race does seem concerning, I would vote for keeping the update in
> > there and disabling preemption around the update, so that hiwater
> > cannot swing back and forth.
> 
> ??  Oleg is _fixing_ a race by removing the update from do_exit();
> and he is fixing the way the hiwater info was collected in tsacct.c.

I see that change and the reasoning seems accurate that we can query
the task at anytime, but I worry that if taskstats is not enabled, we'll
never call update_hiwater.* on the exiting task. 

I wonder if a thread came in and like Oleg said, did (without taskstats
enabled)

free(malloc(some size)), followed by exit()

whether task_mem() would show the correct results for hiwater.*. I
should try it out and look more closely at the code as well.

-- 
	Balbir
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