[RFC,1/6] spinlock: Add library function to allocate spinlock buckets array

Add two new library functions alloc_bucket_spinlocks and
free_bucket_spinlocks. These are use to allocate and free an array
of spinlocks that are useful as locks for hash buckets. The interface
specifies the maximum number of spinlocks in the array as well
as a CPU multiplier to derive the number of spinlocks to allocate.
The number to allocated is rounded up to a power of two to make
the array amenable to hash lookup.

Signed-off-by: Tom Herbert <tom@herbertland.com>
---
 include/linux/spinlock.h |  6 +++++
 lib/Makefile             |  2 +-
 lib/bucket_locks.c       | 63 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 lib/bucket_locks.c

On Fri, 2016-09-09 at 16:19 -0700, Tom Herbert wrote:
> Add two new library functions alloc_bucket_spinlocks and
> free_bucket_spinlocks. These are use to allocate and free an array
> of spinlocks that are useful as locks for hash buckets. The interface
> specifies the maximum number of spinlocks in the array as well
> as a CPU multiplier to derive the number of spinlocks to allocate.
> The number to allocated is rounded up to a power of two to make
> the array amenable to hash lookup.
> 
> Signed-off-by: Tom Herbert <tom@herbertland.com>

I like this idea!!

Reviewed by Greg Rose <grose@lightfleet.com>

> ---
>  include/linux/spinlock.h |  6 +++++
>  lib/Makefile             |  2 +-
>  lib/bucket_locks.c       | 63 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 70 insertions(+), 1 deletion(-)
>  create mode 100644 lib/bucket_locks.c
> 
> diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
> index 47dd0ce..4ebdfbf 100644
> --- a/include/linux/spinlock.h
> +++ b/include/linux/spinlock.h
> @@ -416,4 +416,10 @@ extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
>  #define atomic_dec_and_lock(atomic, lock) \
>  		__cond_lock(lock, _atomic_dec_and_lock(atomic, lock))
>  
> +int alloc_bucket_spinlocks(spinlock_t **locks, unsigned int *lock_mask,
> +			   unsigned int max_size, unsigned int cpu_mult,
> +			   gfp_t gfp);
> +
> +void free_bucket_spinlocks(spinlock_t *locks);
> +
>  #endif /* __LINUX_SPINLOCK_H */
> diff --git a/lib/Makefile b/lib/Makefile
> index cfa68eb..a1dedf1 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -37,7 +37,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
>  	 gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \
>  	 bsearch.o find_bit.o llist.o memweight.o kfifo.o \
>  	 percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o \
> -	 once.o
> +	 once.o bucket_locks.o
>  obj-y += string_helpers.o
>  obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
>  obj-y += hexdump.o
> diff --git a/lib/bucket_locks.c b/lib/bucket_locks.c
> new file mode 100644
> index 0000000..bb9bf11
> --- /dev/null
> +++ b/lib/bucket_locks.c
> @@ -0,0 +1,63 @@
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/vmalloc.h>
> +#include <linux/mm.h>
> +#include <linux/export.h>
> +
> +/* Allocate an array of spinlocks to be accessed by a hash. Two arguments
> + * indicate the number of elements to allocate in the array. max_size
> + * gives the maximum number of elements to allocate. cpu_mult gives
> + * the number of locks per CPU to allocate. The size is rounded up
> + * to a power of 2 to be suitable as a hash table.
> + */
> +int alloc_bucket_spinlocks(spinlock_t **locks, unsigned int *locks_mask,
> +			   unsigned int max_size, unsigned int cpu_mult,
> +			   gfp_t gfp)
> +{
> +	unsigned int i, size;
> +#if defined(CONFIG_PROVE_LOCKING)
> +	unsigned int nr_pcpus = 2;
> +#else
> +	unsigned int nr_pcpus = num_possible_cpus();
> +#endif
> +	spinlock_t *tlocks = NULL;
> +
> +	if (cpu_mult) {
> +		nr_pcpus = min_t(unsigned int, nr_pcpus, 64UL);
> +		size = min_t(unsigned int, nr_pcpus * cpu_mult, max_size);
> +	} else {
> +		size = max_size;
> +	}
> +	size = roundup_pow_of_two(size);
> +
> +	if (!size)
> +		return -EINVAL;
> +
> +	if (sizeof(spinlock_t) != 0) {
> +#ifdef CONFIG_NUMA
> +		if (size * sizeof(spinlock_t) > PAGE_SIZE &&
> +		    gfp == GFP_KERNEL)
> +			tlocks = vmalloc(size * sizeof(spinlock_t));
> +#endif
> +		if (gfp != GFP_KERNEL)
> +			gfp |= __GFP_NOWARN | __GFP_NORETRY;
> +
> +		if (!tlocks)
> +			tlocks = kmalloc_array(size, sizeof(spinlock_t), gfp);
> +		if (!tlocks)
> +			return -ENOMEM;
> +		for (i = 0; i < size; i++)
> +			spin_lock_init(&tlocks[i]);
> +	}
> +	*locks = tlocks;
> +	*locks_mask = size - 1;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(alloc_bucket_spinlocks);
> +
> +void free_bucket_spinlocks(spinlock_t *locks)
> +{
> +	kvfree(locks);
> +}
> +EXPORT_SYMBOL(free_bucket_spinlocks);

On 09/09/16 at 04:19pm, Tom Herbert wrote:
> Add two new library functions alloc_bucket_spinlocks and
> free_bucket_spinlocks. These are use to allocate and free an array
> of spinlocks that are useful as locks for hash buckets. The interface
> specifies the maximum number of spinlocks in the array as well
> as a CPU multiplier to derive the number of spinlocks to allocate.
> The number to allocated is rounded up to a power of two to make
> the array amenable to hash lookup.
> 
> Signed-off-by: Tom Herbert <tom@herbertland.com>

Acked-by: Thomas Graf <tgraf@suug.ch>