Re: weird allocation pattern in alloc_ila_locks

[Michal Hocko <mhocko@kernel.org>]

On Fri 06-01-17 10:51:15, Michal Hocko wrote:
> Hi Tom,
> I am currently looking at kmalloc with vmalloc fallback users [1]
> and came across alloc_ila_locks which is using a pretty unusual
> allocation pattern - it seems to be a c&p alloc_bucket_locks which
> is doing a similar thing - except it has to support GFP_ATOMIC.
> 
> I am really wondering what is the point of 
> #ifdef CONFIG_NUMA
> 		if (size * sizeof(spinlock_t) > PAGE_SIZE)
> 			ilan->locks = vmalloc(size * sizeof(spinlock_t));
> 		else
> #endif
> 
> there doesn't seem to be any NUMA awareness in the ifdef code so I can
> only assume that the intention is to reflect that NUMA machines tend to
> have more CPUs. On the other hand nr_pcpus is limited to 32 so this
> doesn't seem to be the case here...
> Can we just get rid of this ugly and confusing code and do something as
> simple as
> diff --git a/net/ipv6/ila/ila_xlat.c b/net/ipv6/ila/ila_xlat.c
> index af8f52ee7180..1d86ceae61b3 100644
> --- a/net/ipv6/ila/ila_xlat.c
> +++ b/net/ipv6/ila/ila_xlat.c
> @@ -41,13 +41,11 @@ static int alloc_ila_locks(struct ila_net *ilan)
>  	size = roundup_pow_of_two(nr_pcpus * LOCKS_PER_CPU);
>  
>  	if (sizeof(spinlock_t) != 0) {
> -#ifdef CONFIG_NUMA
> -		if (size * sizeof(spinlock_t) > PAGE_SIZE)
> -			ilan->locks = vmalloc(size * sizeof(spinlock_t));
> -		else
> -#endif
>  		ilan->locks = kmalloc_array(size, sizeof(spinlock_t),
> -					    GFP_KERNEL);
> +					    GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
> +		if (!ilan->locks)
> +			ilan->locks = vmalloc(size * sizeof(spinlock_t));
> +
>  		if (!ilan->locks)
>  			return -ENOMEM;
>  		for (i = 0; i < size; i++)
> 
> which I would then simply turn into kvmalloc()?

The patch would look as follows:
---