chengming.zhou@xxxxxxxxx writes:
> From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>
> ```
> hint = nr + 1;
> if (hint >= depth - 1)
> hint = 0;
> ```
>
> Now we wrap the hint to 0 in the failure case, but:
> 1. hint == depth - 1, is actually an available offset hint, which
> we shouldn't wrap hint to 0.
> 2. In the strict round_robin non-wrap case, we shouldn't wrap at all.
>
> ```
> wrap = wrap && hint;
> ```
>
> We only need to check wrap based on the original hint ( > 0), don't need
> to recheck the new hint which maybe updated in the failure case.
> Also delete the mismatched comments by the way.
>
> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> ---
> lib/sbitmap.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index eff4e42c425a..5ed6c2adf58e 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -144,12 +144,7 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
> while (1) {
> nr = find_next_zero_bit(word, depth, hint);
> if (unlikely(nr >= depth)) {
> - /*
> - * We started with an offset, and we didn't reset the
> - * offset to 0 in a failure case, so start from 0 to
> - * exhaust the map.
> - */
> - if (hint && wrap) {
> + if (wrap) {
> hint = 0;
> continue;
I think this is wrong. If you start with an offset in the wrap case and
the bitmap is completely full this will become busy wait until a bit is
available. The hint check is what make you break out of the loop early,
after wrapping, re-walking the entire bitmap and failing to find any
available space.
> @@ -160,8 +155,13 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
> break;
>
> hint = nr + 1;
> - if (hint >= depth - 1)
> - hint = 0;
> + if (hint >= depth) {
> + if (wrap) {
> + hint = 0;
> + continue;
> + }
> + return -1;
> + }
> }
>
> return nr;
--
Gabriel Krisman Bertazi
