Re: [PATCH 16/20] io-controller: IO group refcounting support

Vivek Goyal
2009-06-08T13:54:22Z

On Mon, Jun 08, 2009 at 10:03:24AM +0800, Gui Jianfeng wrote:
> Vivek Goyal wrote:
> ...
> >
> > /**
> > @@ -436,7 +443,6 @@ static void bfq_idle_insert(struct io_service_tree *st,
> > {
> > struct io_entity *first_idle = st->first_idle;
> > struct io_entity *last_idle = st->last_idle;
> > - struct io_queue *ioq = io_entity_to_ioq(entity);
> >
> > if (first_idle == NULL || bfq_gt(first_idle->finish, entity->finish))
> > st->first_idle = entity;
> > @@ -444,10 +450,6 @@ static void bfq_idle_insert(struct io_service_tree *st,
> > st->last_idle = entity;
> >
> > bfq_insert(&st->idle, entity);
> > -
> > - /* Add this queue to idle list */
> > - if (ioq)
> > - list_add(&ioq->queue_list, &ioq->efqd->idle_list);
> > }
> >
> > /**
> > @@ -723,8 +725,26 @@ int __bfq_deactivate_entity(struct io_entity *entity, int requeue)
> > void bfq_deactivate_entity(struct io_entity *entity, int requeue)
> > {
> > struct io_sched_data *sd;
> > + struct io_group *iog;
> > struct io_entity *parent;
> >
> > + iog = container_of(entity->sched_data, struct io_group, sched_data);
> > +
> > + /*
> > + * Hold a reference to entity's iog until we are done. This function
> > + * travels the hierarchy and we don't want to free up the group yet
> > + * while we are traversing the hiearchy. It is possible that this
> > + * group's cgroup has been removed hence cgroup reference is gone.
> > + * If this entity was active entity, then its group will not be on
> > + * any of the trees and it will be freed up the moment queue is
> > + * freed up in __bfq_deactivate_entity().
> > + *
> > + * Hence, hold a reference, deactivate the hierarhcy of entities and
> > + * then drop the reference which should free up the whole chain of
> > + * groups.
> > + */
> > + elv_get_iog(iog);
> > +
> > for_each_entity_safe(entity, parent) {
> > sd = entity->sched_data;
> >
> > @@ -736,21 +756,28 @@ void bfq_deactivate_entity(struct io_entity *entity, int requeue)
> > */
> > break;
> >
> > - if (sd->next_active != NULL)
> > + if (sd->next_active != NULL) {
> > /*
> > * The parent entity is still backlogged and
> > * the budgets on the path towards the root
> > * need to be updated.
> > */
> > + elv_put_iog(iog);
> > goto update;
> > + }
> >
> > /*
> > * If we reach there the parent is no more backlogged and
> > * we want to propagate the dequeue upwards.
> > + *
> > + * If entity's group has been marked for deletion, don't
> > + * requeue the group in idle tree so that it can be freed.
> > */
> > - requeue = 1;
> > + if (!iog_deleting(iog))
> > + requeue = 1;
>
> Hi Vivek,
>
> IIUC, if the iog is marked deleting, all iogs in the hierarchy don't have a chance
> to be requeued into idle trees. So, I wonder why do it like this? Why the upper iogs
> can't be requeued to the idle tree?
>

I think this is a bug Gui. Good catch. I think following should fix it.

Thanks
Vivek

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
block/elevator-fq.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

Index: linux16/block/elevator-fq.c
===================================================================
--- linux16.orig/block/elevator-fq.c 2009-06-06 14:21:11.000000000 -0400
+++ linux16/block/elevator-fq.c 2009-06-08 09:40:59.000000000 -0400
@@ -863,7 +863,7 @@ int __bfq_deactivate_entity(struct io_en
void bfq_deactivate_entity(struct io_entity *entity, int requeue)
{
struct io_sched_data *sd;
- struct io_group *iog;
+ struct io_group *iog, *__iog;
struct io_entity *parent;

iog = container_of(entity->sched_data, struct io_group, sched_data);
@@ -911,8 +911,11 @@ void bfq_deactivate_entity(struct io_ent
* If entity's group has been marked for deletion, don't
* requeue the group in idle tree so that it can be freed.
*/
- if (!iog_deleting(iog))
- requeue = 1;
+ if (parent) {
+ __iog = container_of(parent, struct io_group, entity);
+ if (!iog_deleting(__iog))
+ requeue = 1;
+ }
}

elv_put_iog(iog);