linux-kernel - Re: [PATCH 1/3 v5] kernel/fork.c: new function for max

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Date:	Tue, 24 Feb 2015 14:16:21 -0800 (PST)
From:	David Rientjes <rientjes@...gle.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 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>,
	Oleg Nesterov <oleg@...hat.com>,
	"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 1/3 v5] kernel/fork.c: new function for max_threads

On Tue, 24 Feb 2015, Heinrich Schuchardt wrote:

> > I'm afraid I don't understand this.  The intent of the patch is to 
> > separate the max_threads logic into a new function, correct?  If that's 
> > true, then I don't understand why UINT_MAX is being introduced into this 
> > path and passed to the new function when it is ignored.
> > 
> > I think it would be better to simply keep passing mempages to fork_init() 
> > and then pass it to set_max_threads() where max_threads actually gets set 
> > using the argument passed.  At least, the code would then match the intent 
> > of the patch.
> > 
> Please, read patch 2/3 which provides support for the argument,
> and patch 3/3 that finally needs it.
> 

The problem is with the structure of your patchset.  You want three 
patches.  There's one bugfix patch, a preparation patch, and a feature 
patch.  The bugfix patch should come first so that it can be applied, 
possibly, to stable kernels and doesn't depend on unnecessary preparation 
patches for features.

1/3: change the implementation of fork_init(), with commentary, to avoid 
the divide by zero on certain arches, enforce the limits, and deal with 
variable types to prevent overflow.  This is the most urgent patch and 
fixes a bug.

2/3: simply extract the fixed fork_init() implementation into a new 
set_max_threads() in preparation to use it for threads-max, (hint: 
UINT_MAX and ignored arguments should not appear in this patch),

3/3: use the new set_max_threads() implementation for threads-max with an 
update to the documentation.
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