On Mon, Dec 03, 2018 at 02:56:17PM -0700, Jens Axboe wrote:
> When we are iterating the set bits in a word, we also need to factor in
> the cleared bits. Don't call fn() unless the bit is also not set in
> the cleared word.
>
> Fixes: ea86ea2cdced ("sbitmap: ammortize cost of clearing bits")
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>
> diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
> index 92806a2dbab7..9f374fbcdba6 100644
> --- a/include/linux/sbitmap.h
> +++ b/include/linux/sbitmap.h
> @@ -283,6 +283,11 @@ static inline void __sbitmap_for_each_set(struct sbitmap *sb,
> nr = find_next_bit(&word->word, depth, nr);
> if (nr >= depth)
> break;
> + /* if set in cleared, it's actually free */
> + if (test_bit(nr, &word->cleared)) {
> + nr++;
> + continue;
> + }
> if (!fn(sb, (index << sb->shift) + nr, data))
> return;
>
> --
> Jens Axboe
>
How about something like this:
diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index f0f49bbb2617..fe9122386255 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -265,12 +265,14 @@ static inline void __sbitmap_for_each_set(struct sbitmap *sb,
nr = SB_NR_TO_BIT(sb, start);
while (scanned < sb->depth) {
- struct sbitmap_word *word = &sb->map[index];
- unsigned int depth = min_t(unsigned int, word->depth - nr,
+ unsigned long word;
+ unsigned int depth = min_t(unsigned int,
+ sb->map[index].depth - nr,
sb->depth - scanned);
scanned += depth;
- if (!word->word)
+ word = sb->map[index].word & ~sb->map[index].cleared;
+ if (!word)
goto next;
/*
@@ -280,7 +282,7 @@ static inline void __sbitmap_for_each_set(struct sbitmap *sb,
*/
depth += nr;
while (1) {
- nr = find_next_bit(&word->word, depth, nr);
+ nr = find_next_bit(&word, depth, nr);
if (nr >= depth)
break;
if (!fn(sb, (index << sb->shift) + nr, data))
Might be marginally faster.
