[PATCH v2 08/13] bitmap: introduce generic optimized bitmap_size()
From: Alexander Lobakin
Date: Mon Oct 16 2023 - 13:21:13 EST
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 divides `nbits + 63` 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@xxxxxxxxx>
Acked-by: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
---
drivers/md/dm-clone-metadata.c | 5 -----
drivers/s390/cio/idset.c | 2 +-
include/linux/bitmap.h | 8 +++++---
include/linux/cpumask.h | 2 +-
lib/math/prime_numbers.c | 2 --
tools/include/linux/bitmap.h | 8 +++++---
6 files changed, 12 insertions(+), 15 deletions(-)
diff --git a/drivers/md/dm-clone-metadata.c b/drivers/md/dm-clone-metadata.c
index c43d55672bce..47c1fa7aad8b 100644
--- a/drivers/md/dm-clone-metadata.c
+++ b/drivers/md/dm-clone-metadata.c
@@ -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)
{
diff --git a/drivers/s390/cio/idset.c b/drivers/s390/cio/idset.c
index 0a1105a483bf..e5f28370a903 100644
--- a/drivers/s390/cio/idset.c
+++ b/drivers/s390/cio/idset.c
@@ -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)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index c413e2ecb628..2020cb534ed7 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -241,9 +241,11 @@ extern int bitmap_print_list_to_buf(char *buf, const unsigned long *maskp,
#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;
@@ -253,7 +255,7 @@ 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;
@@ -264,7 +266,7 @@ 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;
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index f10fb87d49db..dbdbf1451cad 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -821,7 +821,7 @@ 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);
}
/*
diff --git a/lib/math/prime_numbers.c b/lib/math/prime_numbers.c
index d42cebf7407f..d3b64b10da1c 100644
--- a/lib/math/prime_numbers.c
+++ b/lib/math/prime_numbers.c
@@ -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;
diff --git a/tools/include/linux/bitmap.h b/tools/include/linux/bitmap.h
index f3566ea0f932..81a2299ace15 100644
--- a/tools/include/linux/bitmap.h
+++ b/tools/include/linux/bitmap.h
@@ -2,6 +2,7 @@
#ifndef _TOOLS_LINUX_BITMAP_H
#define _TOOLS_LINUX_BITMAP_H
+#include <linux/align.h>
#include <string.h>
#include <linux/bitops.h>
#include <linux/find.h>
@@ -25,13 +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));
}
}
@@ -83,7 +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));
}
/*
--
2.41.0