Commit c56f97c5 authored by Yury Norov [NVIDIA]'s avatar Yury Norov [NVIDIA] Committed by Yury Norov
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bitmap: generalize node_random() 



Generalize node_random() and make it available to general bitmaps and
cpumasks users.

Notice, find_first_bit() is generally faster than find_nth_bit(), and we
employ it when there's a single set bit in the bitmap.

See commit 3e061d92 ("lib/nodemask: optimize node_random for
nodemask with single NUMA node").

CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatar"Yury Norov [NVIDIA]" <yury.norov@gmail.com>
parent 73392339

include/linux/find.h

+2 −0
Original line number Diff line number Diff line
@@ -44,6 +44,8 @@ unsigned long _find_next_bit_le(const unsigned long *addr, unsigned 
				long size, unsigned long offset);

#endif



unsigned long find_random_bit(const unsigned long *addr, unsigned long size);



#ifndef find_next_bit

/**

 * find_next_bit - find the next set bit in a memory region

include/linux/nodemask.h

+3 −15
Original line number Diff line number Diff line
@@ -492,21 +492,9 @@ static __always_inline int num_node_state(enum node_states state) 
static __always_inline int node_random(const nodemask_t *maskp)

{

#if defined(CONFIG_NUMA) && (MAX_NUMNODES > 1)

	int w, bit;



	w = nodes_weight(*maskp);

	switch (w) {

	case 0:

		bit = NUMA_NO_NODE;

		break;

	case 1:

		bit = first_node(*maskp);

		break;

	default:

		bit = find_nth_bit(maskp->bits, MAX_NUMNODES, get_random_u32_below(w));

		break;

	}

	return bit;

	int node = find_random_bit(maskp->bits, MAX_NUMNODES);



	return node < MAX_NUMNODES ? node : NUMA_NO_NODE;

#else

	return 0;

#endif

lib/find_bit.c

+24 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
#include <linux/math.h>

#include <linux/minmax.h>

#include <linux/swab.h>

#include <linux/random.h>



/*

 * Common helper for find_bit() function family
@@ -291,3 +292,26 @@ EXPORT_SYMBOL(_find_next_bit_le); 
#endif



#endif /* __BIG_ENDIAN */



/**

 * find_random_bit - find a set bit at random position

 * @addr: The address to base the search on

 * @size: The bitmap size in bits

 *

 * Returns: a position of a random set bit; >= @size otherwise

 */

unsigned long find_random_bit(const unsigned long *addr, unsigned long size)

{

	int w = bitmap_weight(addr, size);



	switch (w) {

	case 0:

		return size;

	case 1:

		/* Performance trick for single-bit bitmaps */

		return find_first_bit(addr, size);

	default:

		return find_nth_bit(addr, size, get_random_u32_below(w));

	}

}

EXPORT_SYMBOL(find_random_bit);