sbitmap: optimise sbitmap_deferred_clear()

Because of spinlocks and atomics sbitmap_deferred_clear() have to reload
&sb->map[index] on each access even though the map address won't change.
Pass in sbitmap_word instead of {sb, index}, so it's cached in a
variable. It also improves code generation of
sbitmap_find_bit_in_index().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 267aa7709416d61343fdbba05788625617786c62..c1c8a4e693251c6bd8d533607697a03f655097ad 100644 (file)
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -12,32 +12,32 @@
 /*
  * See if we have deferred clears that we can batch move
  */
-static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
+static inline bool sbitmap_deferred_clear(struct sbitmap_word *map)
 {
        unsigned long mask, val;
        bool ret = false;
        unsigned long flags;
 
-       spin_lock_irqsave(&sb->map[index].swap_lock, flags);
+       spin_lock_irqsave(&map->swap_lock, flags);
 
-       if (!sb->map[index].cleared)
+       if (!map->cleared)
                goto out_unlock;
 
        /*
         * First get a stable cleared mask, setting the old mask to 0.
         */
-       mask = xchg(&sb->map[index].cleared, 0);
+       mask = xchg(&map->cleared, 0);
 
        /*
         * Now clear the masked bits in our free word
         */
        do {
-               val = sb->map[index].word;
-       } while (cmpxchg(&sb->map[index].word, val, val & ~mask) != val);
+               val = map->word;
+       } while (cmpxchg(&map->word, val, val & ~mask) != val);
 
        ret = true;
 out_unlock:
-       spin_unlock_irqrestore(&sb->map[index].swap_lock, flags);
+       spin_unlock_irqrestore(&map->swap_lock, flags);
        return ret;
 }
 
@@ -92,7 +92,7 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
        unsigned int i;
 
        for (i = 0; i < sb->map_nr; i++)
-               sbitmap_deferred_clear(sb, i);
+               sbitmap_deferred_clear(&sb->map[i]);
 
        sb->depth = depth;
        sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
@@ -139,15 +139,15 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
 static int sbitmap_find_bit_in_index(struct sbitmap *sb, int index,
                                     unsigned int alloc_hint, bool round_robin)
 {
+       struct sbitmap_word *map = &sb->map[index];
        int nr;
 
        do {
-               nr = __sbitmap_get_word(&sb->map[index].word,
-                                       sb->map[index].depth, alloc_hint,
+               nr = __sbitmap_get_word(&map->word, map->depth, alloc_hint,
                                        !round_robin);
                if (nr != -1)
                        break;
-               if (!sbitmap_deferred_clear(sb, index))
+               if (!sbitmap_deferred_clear(map))
                        break;
        } while (1);
 
@@ -207,7 +207,7 @@ again:
                        break;
                }
 
-               if (sbitmap_deferred_clear(sb, index))
+               if (sbitmap_deferred_clear(&sb->map[index]))
                        goto again;
 
                /* Jump to next index. */