[PATCH] lib/sbitmap: kill 'depth' from sbitmap_word

Ming Lei
2022-01-10T01:50:20Z

Only the last sbitmap_word can have different depth, and all the others
must have same depth of 1U << sb->shift, so not necessary to store it in
sbitmap_word, and it can be retrieved easily and efficiently by adding
one internal helper of __map_depth(sb, index).

Not see performance effect when running iops test on null_blk.

This way saves us one cacheline(usually 64 words) per each sbitmap_word.

Cc: Martin Wilck <martin.wilck@suse.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
include/linux/sbitmap.h | 15 +++++++++------
lib/sbitmap.c | 34 ++++++++++++++--------------------
2 files changed, 23 insertions(+), 26 deletions(-)

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index fc0357a6e19b..a2b86760f985 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -27,11 +27,6 @@ struct seq_file;
* struct sbitmap_word - Word in a &struct sbitmap.
*/
struct sbitmap_word {
- /**
- * @depth: Number of bits being used in @word/@cleared
- */
- unsigned long depth;
-
/**
* @word: word holding free bits
*/
@@ -164,6 +159,14 @@ struct sbitmap_queue {
int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
gfp_t flags, int node, bool round_robin, bool alloc_hint);

+/* sbitmap internal helper */
+static inline unsigned int __map_depth(const struct sbitmap *sb, int index)
+{
+ if (index == sb->map_nr - 1)
+ return sb->depth - (index << sb->shift);
+ return 1U << sb->shift;
+}
+
/**
* sbitmap_free() - Free memory used by a &struct sbitmap.
* @sb: Bitmap to free.
@@ -251,7 +254,7 @@ static inline void __sbitmap_for_each_set(struct sbitmap *sb,
while (scanned < sb->depth) {
unsigned long word;
unsigned int depth = min_t(unsigned int,
- sb->map[index].depth - nr,
+ __map_depth(sb, index) - nr,
sb->depth - scanned);

scanned += depth;
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 2709ab825499..e9a51337a2a3 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -85,7 +85,6 @@ int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
bool alloc_hint)
{
unsigned int bits_per_word;
- unsigned int i;

if (shift < 0)
shift = sbitmap_calculate_shift(depth);
@@ -117,10 +116,6 @@ int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
return -ENOMEM;
}

- for (i = 0; i < sb->map_nr; i++) {
- sb->map[i].depth = min(depth, bits_per_word);
- depth -= sb->map[i].depth;
- }
return 0;
}
EXPORT_SYMBOL_GPL(sbitmap_init_node);
@@ -135,11 +130,6 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth)

sb->depth = depth;
sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
-
- for (i = 0; i < sb->map_nr; i++) {
- sb->map[i].depth = min(depth, bits_per_word);
- depth -= sb->map[i].depth;
- }
}
EXPORT_SYMBOL_GPL(sbitmap_resize);

@@ -184,8 +174,8 @@ static int sbitmap_find_bit_in_index(struct sbitmap *sb, int index,
int nr;

do {
- nr = __sbitmap_get_word(&map->word, map->depth, alloc_hint,
- !sb->round_robin);
+ nr = __sbitmap_get_word(&map->word, __map_depth(sb, index),
+ alloc_hint, !sb->round_robin);
if (nr != -1)
break;
if (!sbitmap_deferred_clear(map))
@@ -257,7 +247,9 @@ static int __sbitmap_get_shallow(struct sbitmap *sb,
for (i = 0; i < sb->map_nr; i++) {
again:
nr = __sbitmap_get_word(&sb->map[index].word,
- min(sb->map[index].depth, shallow_depth),
+ min_t(unsigned int,
+ __map_depth(sb, index),
+ shallow_depth),
SB_NR_TO_BIT(sb, alloc_hint), true);
if (nr != -1) {
nr += index << sb->shift;
@@ -315,11 +307,12 @@ static unsigned int __sbitmap_weight(const struct sbitmap *sb, bool set)

for (i = 0; i < sb->map_nr; i++) {
const struct sbitmap_word *word = &sb->map[i];
+ unsigned int word_depth = __map_depth(sb, i);

if (set)
- weight += bitmap_weight(&word->word, word->depth);
+ weight += bitmap_weight(&word->word, word_depth);
else
- weight += bitmap_weight(&word->cleared, word->depth);
+ weight += bitmap_weight(&word->cleared, word_depth);
}
return weight;
}
@@ -367,7 +360,7 @@ void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
for (i = 0; i < sb->map_nr; i++) {
unsigned long word = READ_ONCE(sb->map[i].word);
unsigned long cleared = READ_ONCE(sb->map[i].cleared);
- unsigned int word_bits = READ_ONCE(sb->map[i].depth);
+ unsigned int word_bits = __map_depth(sb, i);

word &= ~cleared;

@@ -508,15 +501,16 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
for (i = 0; i < sb->map_nr; i++) {
struct sbitmap_word *map = &sb->map[index];
unsigned long get_mask;
+ unsigned int map_depth = __map_depth(sb, index);

sbitmap_deferred_clear(map);
- if (map->word == (1UL << (map->depth - 1)) - 1)
+ if (map->word == (1UL << (map_depth - 1)) - 1)
continue;

- nr = find_first_zero_bit(&map->word, map->depth);
- if (nr + nr_tags <= map->depth) {
+ 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);
+ int map_tags = min_t(int, nr_tags, map_depth);
unsigned long val, ret;

get_mask = ((1UL << map_tags) - 1) << nr;
--
2.31.1