linux-kernel - Re: [PATCH 4/4 v4] kernel/fork.c: memory hotplug updates max

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Message-ID: <20150223205052.GA26955@redhat.com>
Date:	Mon, 23 Feb 2015 21:50:52 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Heinrich Schuchardt <xypron.glpk@....de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Aaron Tomlin <atomlin@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Davidlohr Bueso <dave@...olabs.net>,
	David Rientjes <rientjes@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Fabian Frederick <fabf@...net.be>,
	Guenter Roeck <linux@...ck-us.net>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Jens Axboe <axboe@...com>, Joe Perches <joe@...ches.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Kees Cook <keescook@...omium.org>,
	Michael Marineau <mike@...ineau.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vladimir Davydov <vdavydov@...allels.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4 v4] kernel/fork.c: memory hotplug updates
	max_threads

On 02/23, Heinrich Schuchardt wrote:
>
> +static int memory_hotplug_callback(struct notifier_block *self,
> +				   unsigned long action, void *arg)
> +{
> +	switch (action) {
> +	case MEM_ONLINE:
> +		/*
> +		 * If memory was added, try to maximize the number of allowed
> +		 * threads.
> +		 */
> +		set_max_threads(UINT_MAX);
> +		break;
> +	case MEM_OFFLINE:
> +		/*
> +		 * If memory was removed, try to keep current value.
> +		 */
> +		set_max_threads(max_threads);
> +		break;
> +	}

can't understand... set_max_threads() added by 1/4 ignore its argument.
Why does it need "int max_threads_suggested" then?

And it changes the swapper/0's rlimits. This is pointless after we fork
/sbin/init.

It seems to me these patches need some cleanups. Plus I am not sure the
kernel should update max_threads automatically, we have the "threads-max"
sysctl.

Oleg.

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