[PATCH] sbitmap: don't update the allocation hint on clear after resize

From: Omar Sandoval
Date: Sat Sep 17 2016 - 15:21:11 EST

From: Omar Sandoval <osandov@xxxxxx>

If we have a bunch of high-numbered bits allocated and then we resize
the struct sbitmap_queue, when those bits get cleared, we'll update the
hint and then have to re-randomize it repeatedly. Avoid that by checking
that the cleared bit is still a valid hint. No measurable performance
difference in the common case.

Signed-off-by: Omar Sandoval <osandov@xxxxxx>

Small tweak to patch 6 that occurred to me after I sent the series out.
Feel free to fold it in to patch 6 or apply it separately as you see


lib/sbitmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index f736c52..e408089 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -321,7 +321,7 @@ void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
sbitmap_clear_bit(&sbq->sb, nr);
- if (likely(!sbq->round_robin))
+ if (likely(!sbq->round_robin && nr < sbq->sb.depth))
*per_cpu_ptr(sbq->alloc_hint, cpu) = nr;