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

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Date:	Wed, 25 Feb 2015 08:21:12 +0100
From:	Heinrich Schuchardt <xypron.glpk@....de>
To:	Ingo Molnar <mingo@...nel.org>
CC:	David Rientjes <rientjes@...gle.com>,
	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>, 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 24.02.2015 23:16, David Rientjes wrote:
> 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.
> 
Hello Ingo,

the current structure of the patch set is based on your suggestion in
https://lkml.org/lkml/2015/2/22/22

Would you agree with the sequence of patches proposed by David?

Best regards

Heinrich
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