diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/sbitmap.c | 74 |
1 files changed, 45 insertions, 29 deletions
diff --git a/lib/sbitmap.c b/lib/sbitmap.c index d3412984170c..4d188d05db15 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -208,8 +208,28 @@ static int sbitmap_find_bit_in_word(struct sbitmap_word *map, return nr; } +static unsigned int __map_depth_with_shallow(const struct sbitmap *sb, + int index, + unsigned int shallow_depth) +{ + u64 shallow_word_depth; + unsigned int word_depth, reminder; + + word_depth = __map_depth(sb, index); + if (shallow_depth >= sb->depth) + return word_depth; + + shallow_word_depth = word_depth * shallow_depth; + reminder = do_div(shallow_word_depth, sb->depth); + + if (reminder >= (index + 1) * word_depth) + shallow_word_depth++; + + return (unsigned int)shallow_word_depth; +} + static int sbitmap_find_bit(struct sbitmap *sb, - unsigned int depth, + unsigned int shallow_depth, unsigned int index, unsigned int alloc_hint, bool wrap) @@ -218,12 +238,12 @@ static int sbitmap_find_bit(struct sbitmap *sb, int nr = -1; for (i = 0; i < sb->map_nr; i++) { - nr = sbitmap_find_bit_in_word(&sb->map[index], - min_t(unsigned int, - __map_depth(sb, index), - depth), - alloc_hint, wrap); + unsigned int depth = __map_depth_with_shallow(sb, index, + shallow_depth); + if (depth) + nr = sbitmap_find_bit_in_word(&sb->map[index], depth, + alloc_hint, wrap); if (nr != -1) { nr += index << sb->shift; break; @@ -287,7 +307,22 @@ static int __sbitmap_get_shallow(struct sbitmap *sb, return sbitmap_find_bit(sb, shallow_depth, index, alloc_hint, true); } -int sbitmap_get_shallow(struct sbitmap *sb, unsigned long shallow_depth) +/** + * sbitmap_get_shallow() - Try to allocate a free bit from a &struct sbitmap, + * limiting the depth used from each word. + * @sb: Bitmap to allocate from. + * @shallow_depth: The maximum number of bits to allocate from the bitmap. + * + * This rather specific operation allows for having multiple users with + * different allocation limits. E.g., there can be a high-priority class that + * uses sbitmap_get() and a low-priority class that uses sbitmap_get_shallow() + * with a @shallow_depth of (sb->depth >> 1). Then, the low-priority + * class can only allocate half of the total bits in the bitmap, preventing it + * from starving out the high-priority class. + * + * Return: Non-negative allocated bit number if successful, -1 otherwise. + */ +static int sbitmap_get_shallow(struct sbitmap *sb, unsigned long shallow_depth) { int nr; unsigned int hint, depth; @@ -302,7 +337,6 @@ int sbitmap_get_shallow(struct sbitmap *sb, unsigned long shallow_depth) return nr; } -EXPORT_SYMBOL_GPL(sbitmap_get_shallow); bool sbitmap_any_bit_set(const struct sbitmap *sb) { @@ -406,27 +440,9 @@ EXPORT_SYMBOL_GPL(sbitmap_bitmap_show); static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq, unsigned int depth) { - unsigned int wake_batch; - unsigned int shallow_depth; - - /* - * Each full word of the bitmap has bits_per_word bits, and there might - * be a partial word. There are depth / bits_per_word full words and - * depth % bits_per_word bits left over. In bitwise arithmetic: - * - * bits_per_word = 1 << shift - * depth / bits_per_word = depth >> shift - * depth % bits_per_word = depth & ((1 << shift) - 1) - * - * Each word can be limited to sbq->min_shallow_depth bits. - */ - shallow_depth = min(1U << sbq->sb.shift, sbq->min_shallow_depth); - depth = ((depth >> sbq->sb.shift) * shallow_depth + - min(depth & ((1U << sbq->sb.shift) - 1), shallow_depth)); - wake_batch = clamp_t(unsigned int, depth / SBQ_WAIT_QUEUES, 1, - SBQ_WAKE_BATCH); - - return wake_batch; + return clamp_t(unsigned int, + min(depth, sbq->min_shallow_depth) / SBQ_WAIT_QUEUES, + 1, SBQ_WAKE_BATCH); } int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth, |