Subject: Re: [PATCH RFC 1/6] spinlock: Add library function to allocate spinlock buckets array

From: Greg <[email-masked]>
Date: Mon, 12 Sep 2016 08:17:46 -0700

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 <[email-masked]>

I like this idea!!

Reviewed by Greg Rose <[email-masked]>

> ---
>  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);