linux-kernel - Re: [PATCH] mm: sync rss-counters at the end of exit

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Message-ID: <CAHGf_=oWj-hz-E5ht8-hUbQKdsZ1bzP80n987kGYnFm8BpXBVQ@mail.gmail.com>
Date:	Mon, 9 Apr 2012 17:04:56 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	Markus Trippelsdorf <markus@...ppelsdorf.de>
Subject: Re: [PATCH] mm: sync rss-counters at the end of exit_mm()

On Mon, Apr 9, 2012 at 4:03 PM, Konstantin Khlebnikov
<khlebnikov@...nvz.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. 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.


>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> Reported-by: Markus Trippelsdorf <markus@...ppelsdorf.de>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  kernel/exit.c |    1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index d8bd3b42..8e09dbe 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -683,6 +683,7 @@ static void exit_mm(struct task_struct * tsk)
>        enter_lazy_tlb(mm, current);
>        task_unlock(tsk);
>        mm_update_next_owner(mm);
> +       sync_mm_rss(mm);
>        mmput(mm);
>  }
>
>
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