To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] simplify/fix first_tid()
References: <441DB045.87C4134C@tv-sign.ru>
	<m1fyldvvvo.fsf@ebiederm.dsl.xmission.com>
	<441EF4D7.AEC1AE8C@tv-sign.ru>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: Mon, 20 Mar 2006 11:56:56 -0700
In-Reply-To: <441EF4D7.AEC1AE8C@tv-sign.ru> (Oleg Nesterov's message of
 "Mon, 20 Mar 2006 21:30:47 +0300")
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Oleg Nesterov <oleg@tv-sign.ru> writes:

> "Eric W. Biederman" wrote:
>> This is better however if I read this code correctly.  It modifies
>> the code so the last time user space goes trough this loop
>> with nr > nr_threads.  Then we will walk the entire threads
>> list to achieve nothing.
>
> This can happen only if the thread we stopped at has exited, and
> some other threads have exited too, so that nr >= ->signal->count.
>
> I think it's not worth optimizing this rare and anyway slow path.
> However, you are the code author, I'll send a trivial patch which
> restores this optimization if you don't change you mind.
>
>> So we really still need the nr_threads test in there so we don't
>> traverse the list twice everytime through readdir.
>
> How so? We don't do it twice?

In general user space does.  Because a read of 0 bytes signifies
the end of a directory.

So we have 2 trips through proc_task_readdir initiated by user
space.

Eric
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