[PATCH 1/9] lib/bitmap: add bitmap_weight_{eq,gt,le}

Yury Norov
2021-11-28T03:59:18Z

Many kernel users call bitmap_weight() to compare the result against
some number or expression:
if (bitmap_weight(...) > 1)
do_something();

It works OK, but may be significantly improved for large bitmaps: if
first few words count set bits to a number greater than given, we can
stop counting and immediately return.

The same idea would work in other direction: if we know that the number
of set bits that we counted so far is small enough, so that it would be
smaller than required number even if all bits of the rest of the bitmap
are set, we can return earlier.

This patch adds new bitmap_weight_{eq,gt,le} functions to allow this
optimization, and the following patches apply them where appropriate.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
include/linux/bitmap.h | 33 ++++++++++++++++++++++
lib/bitmap.c | 63 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 96 insertions(+)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 7dba0847510c..996041f771c8 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -51,6 +51,9 @@ struct device;
* bitmap_empty(src, nbits) Are all bits zero in *src?
* bitmap_full(src, nbits) Are all bits set in *src?
* bitmap_weight(src, nbits) Hamming Weight: number set bits
+ * bitmap_weight_eq(src, nbits, num) Hamming Weight is equal to num
+ * bitmap_weight_gt(src, nbits, num) Hamming Weight is greater than num
+ * bitmap_weight_le(src, nbits, num) Hamming Weight is less than num
* bitmap_set(dst, pos, nbits) Set specified bit area
* bitmap_clear(dst, pos, nbits) Clear specified bit area
* bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free area
@@ -162,6 +165,9 @@ int __bitmap_intersects(const unsigned long *bitmap1,
int __bitmap_subset(const unsigned long *bitmap1,
const unsigned long *bitmap2, unsigned int nbits);
int __bitmap_weight(const unsigned long *bitmap, unsigned int nbits);
+bool __bitmap_weight_eq(const unsigned long *bitmap, unsigned int nbits, unsigned int num);
+bool __bitmap_weight_gt(const unsigned long *bitmap, unsigned int nbits, unsigned int num);
+bool __bitmap_weight_le(const unsigned long *bitmap, unsigned int nbits, unsigned int num);
void __bitmap_set(unsigned long *map, unsigned int start, int len);
void __bitmap_clear(unsigned long *map, unsigned int start, int len);

@@ -403,6 +409,33 @@ static __always_inline int bitmap_weight(const unsigned long *src, unsigned int
return __bitmap_weight(src, nbits);
}

+static __always_inline bool bitmap_weight_eq(const unsigned long *src,
+ unsigned int nbits, unsigned int num)
+{
+ if (small_const_nbits(nbits))
+ return hweight_long(*src & BITMAP_LAST_WORD_MASK(nbits)) == num;
+
+ return __bitmap_weight_eq(src, nbits, num);
+}
+
+static __always_inline bool bitmap_weight_gt(const unsigned long *src,
+ unsigned int nbits, unsigned int num)
+{
+ if (small_const_nbits(nbits))
+ return hweight_long(*src & BITMAP_LAST_WORD_MASK(nbits)) > num;
+
+ return __bitmap_weight_gt(src, nbits, num);
+}
+
+static __always_inline bool bitmap_weight_le(const unsigned long *src,
+ unsigned int nbits, unsigned int num)
+{
+ if (small_const_nbits(nbits))
+ return hweight_long(*src & BITMAP_LAST_WORD_MASK(nbits)) < num;
+
+ return __bitmap_weight_le(src, nbits, num);
+}
+
static __always_inline void bitmap_set(unsigned long *map, unsigned int start,
unsigned int nbits)
{
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 926408883456..72e7ab2d7bdd 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -348,6 +348,69 @@ int __bitmap_weight(const unsigned long *bitmap, unsigned int bits)
}
EXPORT_SYMBOL(__bitmap_weight);

+bool __bitmap_weight_eq(const unsigned long *bitmap, unsigned int bits, unsigned int num)
+{
+ unsigned int k, w, lim = bits / BITS_PER_LONG;
+
+ for (k = 0, w = 0; k < lim; k++) {
+ if (w + bits - k * BITS_PER_LONG < num)
+ return false;
+
+ w += hweight_long(bitmap[k]);
+
+ if (w > num)
+ return false;
+ }
+
+ if (bits % BITS_PER_LONG)
+ w += hweight_long(bitmap[k] & BITMAP_LAST_WORD_MASK(bits));
+
+ return w == num;
+}
+EXPORT_SYMBOL(__bitmap_weight_eq);
+
+bool __bitmap_weight_gt(const unsigned long *bitmap, unsigned int bits, unsigned int num)
+{
+ unsigned int k, w, lim = bits / BITS_PER_LONG;
+
+ for (k = 0, w = 0; k < lim; k++) {
+ if (w + bits - k * BITS_PER_LONG <= num)
+ return false;
+
+ w += hweight_long(bitmap[k]);
+
+ if (w > num)
+ return true;
+ }
+
+ if (bits % BITS_PER_LONG)
+ w += hweight_long(bitmap[k] & BITMAP_LAST_WORD_MASK(bits));
+
+ return w > num;
+}
+EXPORT_SYMBOL(__bitmap_weight_gt);
+
+bool __bitmap_weight_le(const unsigned long *bitmap, unsigned int bits, unsigned int num)
+{
+ unsigned int k, w, lim = bits / BITS_PER_LONG;
+
+ for (k = 0, w = 0; k < lim; k++) {
+ if (w + bits - k * BITS_PER_LONG < num)
+ return true;
+
+ w += hweight_long(bitmap[k]);
+
+ if (w >= num)
+ return false;
+ }
+
+ if (bits % BITS_PER_LONG)
+ w += hweight_long(bitmap[k] & BITMAP_LAST_WORD_MASK(bits));
+
+ return w < num;
+}
+EXPORT_SYMBOL(__bitmap_weight_le);
+
void __bitmap_set(unsigned long *map, unsigned int start, int len)
{
unsigned long *p = map + BIT_WORD(start);
--
2.25.1