Re: [PATCH] blockgroup_lock: hashed spinlocks for ext2 and ext3

[Andi Kleen]

On Sun, 2003-04-13 at 12:00, Linux Kernel Mailing List wrote:

[....]
> 	
> 	These locks are actually fairly generic.  However I presented it as something
> 	which is specific to ext2 and ext3 so that people wouldn't go using them all
> 	over the place.  They consume a lot of storage.
> 

> +
> +struct bgl_lock {
> +	spinlock_t lock;
> +} ____cacheline_aligned_in_smp;
> +
> +struct blockgroup_lock {
> +	struct bgl_lock locks[NR_BG_LOCKS];
> +};

Why don't you use per_cpu data for this ? It can be indexed as well
with per_cpu() and it would safe a lot of space because the padding
would not be all wasted. If you want more than NR_CPUS locks it could be
done using a simple two level index scheme.

-Andi