On Mon, Sep 19, 2016 at 10:48:49AM -0700, Omar Sandoval wrote:
> On Sun, Sep 18, 2016 at 09:37:14AM +0200, Alexander Gordeev wrote:
> > Currently maximum number of used hardware queues is limited to
> > number of CPUs in the system. However, using 'nr_cpu_ids' as
> > the limit for (de-)allocations of data structures instead of
> > existing data structures' counters (a) worsens readability and
> > (b) leads to unused memory when number of hardware queues is
> > less than number of CPUs.
> > 
> > CC: linux-block@vger.kernel.org
> > Signed-off-by: Alexander Gordeev <agord...@redhat.com>
> > ---
> >  block/blk-mq.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 276ec7b..2c77b68 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -2054,8 +2054,8 @@ struct request_queue 
> > *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
> >     if (!q->queue_ctx)
> >             goto err_exit;
> >  
> > -   q->queue_hw_ctx = kzalloc_node(nr_cpu_ids * sizeof(*(q->queue_hw_ctx)),
> > -                                           GFP_KERNEL, set->numa_node);
> > +   q->queue_hw_ctx = kzalloc_node(set->nr_hw_queues *
> > +                   sizeof(*(q->queue_hw_ctx)), GFP_KERNEL, set->numa_node);
> >     if (!q->queue_hw_ctx)
> >             goto err_percpu;
> >  
> > @@ -2319,7 +2319,7 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
> >     if (set->nr_hw_queues > nr_cpu_ids)
> >             set->nr_hw_queues = nr_cpu_ids;
> >  
> > -   set->tags = kzalloc_node(nr_cpu_ids * sizeof(struct blk_mq_tags *),
> > +   set->tags = kzalloc_node(set->nr_hw_queues * sizeof(*set->tags),
> >                              GFP_KERNEL, set->numa_node);
> >     if (!set->tags)
> >             return -ENOMEM;
> > @@ -2360,7 +2360,7 @@ void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
> >  {
> >     int i;
> >  
> > -   for (i = 0; i < nr_cpu_ids; i++) {
> > +   for (i = 0; i < set->nr_hw_queues; i++) {
> >             if (set->tags[i])
> >                     blk_mq_free_rq_map(set, set->tags[i], i);
> >     }
> 
> I don't think this is safe since we might increase the number of
> hardware queues (blk_mq_update_nr_hw_queues()).

It is safe, because blk_mq_update_nr_hw_queues() limits number of
hardware queues to nr_cpu_ids. But still using nr_cpu_ids is wrong,
because (a) set->nr_hw_queues could be less than nr_cpu_ids and
(b) it is set->nr_hw_queues counter that tracks size of the array.

> -- 
> Omar
--
To unsubscribe from this list: send the line "unsubscribe linux-block" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Reply via email to