linux-kernel - Re: [PATCH 1/2] mm: set task exit code before complete_vfork

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Message-ID: <20120420204129.GA8034@redhat.com>
Date:	Fri, 20 Apr 2012 22:41:29 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 1/2] mm: set task exit code before complete_vfork_done()

On 04/20, Konstantin Khlebnikov wrote:
>
> Oleg Nesterov wrote:
>>
>> 	/* sync mm's RSS info before statistics gathering */
>> 	if (tsk->mm)
>> 		sync_mm_rss(tsk->mm);
>>
>> Which "statistics gathering" ? Probably I missed something, but
>> after the quick grep it seems to me that this is only needed for
>> taskstats_exit()->xacct_add_tsk().
>>
>> So why we can't simply add sync_mm_rss() into xacct_add_tsk() ?
>
>> Yes, this way we do not "account" put_user(clear_child_tid) but
>> I think we do not care.
>
> Why we don't care? Each thread can corrupt these counters by one.
> I do not think that we are satisfied with nearly accurate rss accounting.
> +/- one page for each clone()-exit().

Not actually "for each" in practice. Each exit does sync_ (with
this patch from xacct_add_tsk), the net effect should be small.

And. This is what we do now, nobody ever complained.

>> IOW, what do you think about the trivial patch below? Uncompiled,
>> untested, probably incomplete. acct_update_integrals() looks
>> suspicious too.
>
> what a mess! =)

Thanks ;)

But it is much, much simpler than your patches, don't you agree?

Oleg.

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