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Date: Tue, 10 Apr 2012 09:33:38 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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To: Hugh Dickins <hughd@google.com>
CC: KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Konstantin Khlebnikov <khlebnikov@openvz.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Markus Trippelsdorf <markus@trippelsdorf.de>
Subject: Re: [PATCH] mm: sync rss-counters at the end of exit_mm()
References: <20120409200336.8368.63793.stgit@zurg> <CAHGf_=oWj-hz-E5ht8-hUbQKdsZ1bzP80n987kGYnFm8BpXBVQ@mail.gmail.com> <alpine.LSU.2.00.1204091433380.1859@eggly.anvils>
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(2012/04/10 7:03), Hugh Dickins wrote:

> On Mon, 9 Apr 2012, KOSAKI Motohiro wrote:
>> On Mon, Apr 9, 2012 at 4:03 PM, Konstantin Khlebnikov
>> <khlebnikov@openvz.org> wrote:
>>> On task's exit do_exit() calls sync_mm_rss() but this is not enough,
>>> there can be page-faults after this point, for example exit_mm() ->
>>> mm_release() -> put_user() (for processing tsk->clear_child_tid).
>>> Thus there may be some rss-counters delta in current->rss_stat.
>>
>> Seems reasonable.
> 
> Yes, I think Konstantin has probably caught it;
> but I'd like to hear confirmation from Markus.
> 
>> but I have another question. Do we have any reason to
>> keep sync_mm_rss() in do_exit()? I havn't seen any reason that thread exiting
>> makes rss consistency.
> 
> IIRC it's all about the hiwater_rss/maxrss stuff: we want to sync the
> maximum rss into mm->hiwater_rss before it's transferred to signal->maxrss,
> and later made visible to the user though getrusage(RUSAGE_CHILDREN,) -
> does your reading confirm that?
> 


IIRC, sync_mm_rss() in do_exit() is for synchronizing rsscounter for taskacct.
mm->maxrss is sent to listener by xacct_add_tsk(). It's needed to be
synchronized before taskstat_exit()..

Hm, but, exit_mm() is placed after taskstat_exit().

Thanks,
-Kame