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

Heinrich Schuchardt
2015-02-24T21:25:34Z

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