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bitmap: introduce generic optimized bitmap_size() 

The number of times yet another open coded
`BITS_TO_LONGS(nbits) * sizeof(long)` can be spotted is huge.
Some generic helper is long overdue.

Add one, bitmap_size(), but with one detail.
BITS_TO_LONGS() uses DIV_ROUND_UP(). The latter works well when both
divident and divisor are compile-time constants or when the divisor
is not a pow-of-2. When it is however, the compilers sometimes tend
to generate suboptimal code (GCC 13):

48 83 c0 3f          	add    $0x3f,%rax
48 c1 e8 06          	shr    $0x6,%rax
48 8d 14 c5 00 00 00 00	lea    0x0(,%rax,8),%rdx

%BITS_PER_LONG is always a pow-2 (either 32 or 64), but GCC still does
full division of `nbits + 63` by it and then multiplication by 8.
Instead of BITS_TO_LONGS(), use ALIGN() and then divide by 8. GCC:

8d 50 3f             	lea    0x3f(%rax),%edx
c1 ea 03             	shr    $0x3,%edx
81 e2 f8 ff ff 1f    	and    $0x1ffffff8,%edx

Now it shifts `nbits + 63` by 3 positions (IOW performs fast division
by 8) and then masks bits[2:0]. bloat-o-meter:

add/remove: 0/0 grow/shrink: 20/133 up/down: 156/-773 (-617)

Clang does it better and generates the same code before/after starting
from -O1, except that with the ALIGN() approach it uses %edx and thus
still saves some bytes:

add/remove: 0/0 grow/shrink: 9/133 up/down: 18/-538 (-520)

Note that we can't expand DIV_ROUND_UP() by adding a check and using
this approach there, as it's used in array declarations where
expressions are not allowed.
Add this helper to tools/ as well.

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Acked-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexander Lobakin 2024-03-27 16:23:49 +01:00 committed by David S. Miller
parent 10a04ff09b
commit a37fbe666c
6 changed files with 11 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
drivers/md/dm-clone-metadata.c
View File

@ -465,11 +465,6 @@ static void __destroy_persistent_data_structures(struct dm_clone_metadata *cmd)
/*---------------------------------------------------------------------------*/
static size_t bitmap_size(unsigned long nr_bits)
{
return BITS_TO_LONGS(nr_bits) * sizeof(long);
}
static int __dirty_map_init(struct dirty_map *dmap, unsigned long nr_words,
unsigned long nr_regions)
{

2
drivers/s390/cio/idset.c
View File

@ -18,7 +18,7 @@ struct idset {
static inline unsigned long idset_bitmap_size(int num_ssid, int num_id)
{
return BITS_TO_LONGS(num_ssid * num_id) * sizeof(unsigned long);
return bitmap_size(size_mul(num_ssid, num_id));
}
static struct idset *idset_new(int num_ssid, int num_id)

8
include/linux/bitmap.h
View File

@ -226,9 +226,11 @@ void bitmap_fold(unsigned long *dst, const unsigned long *orig,
#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
#define bitmap_size(nbits) (ALIGN(nbits, BITS_PER_LONG) / BITS_PER_BYTE)
static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
{
unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
unsigned int len = bitmap_size(nbits);
if (small_const_nbits(nbits))
*dst = 0;
@ -238,7 +240,7 @@ static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
static inline void bitmap_fill(unsigned long *dst, unsigned int nbits)
{
unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
unsigned int len = bitmap_size(nbits);
if (small_const_nbits(nbits))
*dst = ~0UL;
@ -249,7 +251,7 @@ static inline void bitmap_fill(unsigned long *dst, unsigned int nbits)
static inline void bitmap_copy(unsigned long *dst, const unsigned long *src,
unsigned int nbits)
{
unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
unsigned int len = bitmap_size(nbits);
if (small_const_nbits(nbits))
*dst = *src;

2
include/linux/cpumask.h
View File

@ -853,7 +853,7 @@ static inline int cpulist_parse(const char *buf, struct cpumask *dstp)
*/
static inline unsigned int cpumask_size(void)
{
return BITS_TO_LONGS(large_cpumask_bits) * sizeof(long);
return bitmap_size(large_cpumask_bits);
}
/*

2
lib/math/prime_numbers.c
View File

@ -6,8 +6,6 @@
#include <linux/prime_numbers.h>
#include <linux/slab.h>
#define bitmap_size(nbits) (BITS_TO_LONGS(nbits) * sizeof(unsigned long))
struct primes {
struct rcu_head rcu;
unsigned long last, sz;

7
tools/include/linux/bitmap.h
View File

@ -26,13 +26,14 @@ bool __bitmap_intersects(const unsigned long *bitmap1,
#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
#define bitmap_size(nbits) (ALIGN(nbits, BITS_PER_LONG) / BITS_PER_BYTE)
static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
{
if (small_const_nbits(nbits))
*dst = 0UL;
else {
int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
memset(dst, 0, len);
memset(dst, 0, bitmap_size(nbits));
}
}
@ -84,7 +85,7 @@ static inline void bitmap_or(unsigned long *dst, const unsigned long *src1,
*/
static inline unsigned long *bitmap_zalloc(int nbits)
{
return calloc(1, BITS_TO_LONGS(nbits) * sizeof(unsigned long));
return calloc(1, bitmap_size(nbits));
}
/*