lib/sbitmap: kill 'depth' from sbitmap_word

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).

Remove 'depth' field from sbitmap_word, then the annotation of
____cacheline_aligned_in_smp for 'word' isn't needed any more.

Not see performance effect when running high parallel 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>
Reviewed-by: Martin Wilck <mwilck@suse.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/20220110072945.347535-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 95df357..df3b584 100644 (file)
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -28,14 +28,9 @@ struct seq_file;
  */
 struct sbitmap_word {
        /**
-        * @depth: Number of bits being used in @word/@cleared
-        */
-       unsigned long depth;
-
-       /**
         * @word: word holding free bits
         */
-       unsigned long word ____cacheline_aligned_in_smp;
+       unsigned long word;
 
        /**
         * @cleared: word holding cleared 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 09d293c..b7cb96a 100644 (file)
--- 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;
 
@@ -531,15 +524,16 @@ 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;