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

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Date:	Tue, 24 Feb 2015 13:03:58 -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:

> diff --git a/init/main.c b/init/main.c
> index 61b99376..21394ec 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -94,7 +94,7 @@
>  static int kernel_init(void *);
>  
>  extern void init_IRQ(void);
> -extern void fork_init(unsigned long);
> +extern void fork_init(void);
>  extern void radix_tree_init(void);
>  #ifndef CONFIG_DEBUG_RODATA
>  static inline void mark_rodata_ro(void) { }
> @@ -655,7 +655,7 @@ asmlinkage __visible void __init start_kernel(void)
>  #endif
>  	thread_info_cache_init();
>  	cred_init();
> -	fork_init(totalram_pages);
> +	fork_init();
>  	proc_caches_init();
>  	buffer_init();
>  	key_init();
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 4dc2dda..460b044 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -253,7 +253,27 @@ EXPORT_SYMBOL_GPL(__put_task_struct);
>  
>  void __init __weak arch_task_cache_init(void) { }
>  
> -void __init fork_init(unsigned long mempages)
> +/*
> + * set_max_threads
> + * The argument is ignored.
> + */
> +static void set_max_threads(unsigned int max_threads_suggested)
> +{
> +	/*
> +	 * The default maximum number of threads is set to a safe
> +	 * value: the thread structures can take up at most half
> +	 * of memory.
> +	 */
> +	max_threads = totalram_pages / (8 * THREAD_SIZE / PAGE_SIZE);
> +
> +	/*
> +	 * we need to allow at least 20 threads to boot a system
> +	 */
> +	if (max_threads < 20)
> +		max_threads = 20;
> +}
> +
> +void __init fork_init(void)
>  {
>  #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
>  #ifndef ARCH_MIN_TASKALIGN
> @@ -268,18 +288,7 @@ void __init fork_init(unsigned long mempages)
>  	/* do the arch specific task caches init */
>  	arch_task_cache_init();
>  
> -	/*
> -	 * The default maximum number of threads is set to a safe
> -	 * value: the thread structures can take up at most half
> -	 * of memory.
> -	 */
> -	max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
> -
> -	/*
> -	 * we need to allow at least 20 threads to boot a system
> -	 */
> -	if (max_threads < 20)
> -		max_threads = 20;
> +	set_max_threads(UINT_MAX);
>  
>  	init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
>  	init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;

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.
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