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sbitmap: add __sbitmap_queue_get_batch()

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The block layer tag allocation batching still calls into sbitmap to get
each tag, but we can improve on that. Add __sbitmap_queue_get_batch(),
which returns a mask of tags all at once, along with an offset for
those tags.

An example return would be 0xff, where bits 0..7 are set, with
tag_offset == 128. The valid tags in this case would be 128..135.

A batch is specific to an individual sbitmap_map, hence it cannot be
larger than that. The requested number of tags is automatically reduced
to the max that can be satisfied with a single map.

On failure, 0 is returned. Caller should fall back to single tag
allocation at that point/

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2021-10-09 13:02:23 -06:00
parent 8971a3b7f1
commit 9672b0d437
2 changed files with 64 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

13
include/linux/sbitmap.h
View file

@ -426,6 +426,19 @@ void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth);
*/
int __sbitmap_queue_get(struct sbitmap_queue *sbq);
/**
* __sbitmap_queue_get_batch() - Try to allocate a batch of free bits
* @sbq: Bitmap queue to allocate from.
* @nr_tags: number of tags requested
* @offset: offset to add to returned bits
*
* Return: Mask of allocated tags, 0 if none are found. Each tag allocated is
* a bit in the mask returned, and the caller must add @offset to the value to
* get the absolute tag value.
*/
unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
unsigned int *offset);
/**
* __sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct
* sbitmap_queue, limiting the depth used from each word, with preemption

51
lib/sbitmap.c
View file

@ -489,6 +489,57 @@ int __sbitmap_queue_get(struct sbitmap_queue *sbq)
}
EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
unsigned int *offset)
{
struct sbitmap *sb = &sbq->sb;
unsigned int hint, depth;
unsigned long index, nr;
int i;
if (unlikely(sb->round_robin))
return 0;
depth = READ_ONCE(sb->depth);
hint = update_alloc_hint_before_get(sb, depth);
index = SB_NR_TO_INDEX(sb, hint);
for (i = 0; i < sb->map_nr; i++) {
struct sbitmap_word *map = &sb->map[index];
unsigned long get_mask;
sbitmap_deferred_clear(map);
if (map->word == (1UL << (map->depth - 1)) - 1)
continue;
nr = find_first_zero_bit(&map->word, map->depth);
if (nr + nr_tags <= map->depth) {
atomic_long_t *ptr = (atomic_long_t *) &map->word;
int map_tags = min_t(int, nr_tags, map->depth);
unsigned long val, ret;
get_mask = ((1UL << map_tags) - 1) << nr;
do {
val = READ_ONCE(map->word);
ret = atomic_long_cmpxchg(ptr, val, get_mask | val);
} while (ret != val);
get_mask = (get_mask & ~ret) >> nr;
if (get_mask) {
*offset = nr + (index << sb->shift);
update_alloc_hint_after_get(sb, depth, hint,
*offset + map_tags - 1);
return get_mask;
}
}
/* Jump to next index. */
if (++index >= sb->map_nr)
index = 0;
}
return 0;
}
int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
unsigned int shallow_depth)
{