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From:   Alexander Lobakin <aleksander.lobakin@intel.com>
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Alexander Lobakin <aleksander.lobakin@intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Alexander Potapenko <glider@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        David Ahern <dsahern@kernel.org>,
        Przemek Kitszel <przemyslaw.kitszel@intel.com>,
        Simon Horman <simon.horman@corigine.com>,
        netdev@vger.kernel.org, linux-btrfs@vger.kernel.org,
        dm-devel@redhat.com, ntfs3@lists.linux.dev,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 08/14] bitmap: introduce generic optimized bitmap_size()
Date:   Mon,  9 Oct 2023 17:10:20 +0200
Message-ID: <20231009151026.66145-9-aleksander.lobakin@intel.com>
In-Reply-To: <20231009151026.66145-1-aleksander.lobakin@intel.com>
References: <20231009151026.66145-1-aleksander.lobakin@intel.com>
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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@intel.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 drivers/md/dm-clone-metadata.c | 5 -----
 include/linux/bitmap.h         | 8 +++++---
 include/linux/cpumask.h        | 2 +-
 lib/math/prime_numbers.c       | 2 --
 tools/include/linux/bitmap.h   | 8 +++++---
 5 files changed, 11 insertions(+), 14 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/include/linux/bitmap.h b/include/linux/bitmap.h
index 03644237e1ef..63e422f8ba3d 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -237,9 +237,11 @@ 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;
@@ -249,7 +251,7 @@ 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;
@@ -260,7 +262,7 @@ 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