On 12/3/18 3:05 PM, Omar Sandoval wrote:
> 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 <[email protected]>
>>
>> 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.
Yeah that looks fine as well, tests out good too.
--
Jens Axboe
