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

--
Regards
Gui Jianfeng




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