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

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Date:	Tue, 24 Feb 2015 22:23:28 +0100
From:	Heinrich Schuchardt <xypron.glpk@....de>
To:	David Rientjes <rientjes@...gle.com>
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 24.02.2015 22:03, David Rientjes wrote:
> 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.
> 
Please, read patch 2/3 which provides support for the argument,
and patch 3/3 that finally needs it.

Best regards

Heinrich

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