tree 93751c669d2cba783d4762127efa949ad4bda5f9
parent 98d95416dbfaf4910caadfb4ddc75e4aacbdff8c
author Omar Sandoval <osandov@fb.com> 1474100906 -0700
committer Jens Axboe <axboe@fb.com> 1474123156 -0600

sbitmap: re-initialize allocation hints after resize

After a struct sbitmap_queue is resized smaller, the allocation hints
may still be set to bits beyond the new depth of the bitmap. This means
that, for example, if the number of blk-mq tags is reduced through
sysfs, more requests than the nominal queue depth may be in flight.

It's tempting to fix this at resize time by doing a one-time
reinitialization of the hints, but this can race with
__sbitmap_queue_get() updating the hint. Instead, check the hint before
we use it. This caused no measurable performance difference in my
synthetic benchmarks.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>