linux-kernel - Re: [PATCH v2 1/2] Make the batch size of the percpu

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Message-Id: <20130522002020.60c3808f.akpm@linux-foundation.org>
Date:	Wed, 22 May 2013 00:20:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Ric Mason <ric.masonn@...il.com>,
	Simon Jeons <simon.jeons@...il.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <ak@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/2] Make the batch size of the percpu_counter
 configurable

On Tue, 21 May 2013 17:43:10 -0700 Tim Chen <tim.c.chen@...ux.intel.com> wrote:

> 
> I'll spin off another version of the patch later to add the
> memory-hotplug notifier.  In the mean time, does the following looks
> good to you?
> 
> ...
>
> --- a/include/linux/mman.h
> +++ b/include/linux/mman.h
> @@ -10,12 +10,30 @@
>  extern int sysctl_overcommit_memory;
>  extern int sysctl_overcommit_ratio;
>  extern struct percpu_counter vm_committed_as;
> +#ifdef CONFIG_SMP
> +extern int vm_committed_as_batch;
> +
> +static inline void mm_compute_batch(void)
> +{
> +        int nr = num_present_cpus();
> +        int batch = max(32, nr*2);
> +
> +        /* batch size set to 0.4% of (total memory/#cpus) */
> +        vm_committed_as_batch = max((int) (totalram_pages/nr) / 256, batch);

Use max_t() here.

That expression will overflow when the machine has two exabytes of RAM ;)

> +}
> +#else
> +#define vm_committed_as_batch 0
> +
> +static inline void mm_compute_batch(void)
> +{
> +}
> +#endif

I think it would be better if all the above was not inlined.  There's
no particular reason to inline it, and putting it here requires that
mman.h include a bunch more header files (which the patch forgot to
do).

>  unsigned long vm_memory_committed(void);
>  
>  static inline void vm_acct_memory(long pages)
>  {
> -	percpu_counter_add(&vm_committed_as, pages);
> +	__percpu_counter_add(&vm_committed_as, pages, vm_committed_as_batch);
>  }
>  
>  static inline void vm_unacct_memory(long pages)
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f681e18..55c8773 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3145,11 +3145,15 @@ void mm_drop_all_locks(struct mm_struct *mm)
>  /*
>   * initialise the VMA slab
>   */
> +
> +int vm_committed_as_batch;
> +
>  void __init mmap_init(void)
>  {
>  	int ret;
>  
>  	ret = percpu_counter_init(&vm_committed_as, 0);
> +	mm_compute_batch();
>  	VM_BUG_ON(ret);
>  }
>  
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 298884d..9ad16ba 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -527,11 +527,15 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
>  /*
>   * initialise the VMA and region record slabs
>   */
> +
> +int vm_committed_as_batch;

This definition duplicates the one in mmap.c?

>  void __init mmap_init(void)
>  {
>  	int ret;
>  
>  	ret = percpu_counter_init(&vm_committed_as, 0);
> +	mm_compute_batch();
>  	VM_BUG_ON(ret);
>  	vm_region_jar = KMEM_CACHE(vm_region, SLAB_PANIC);
>  }

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