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blkcg: rename blkcg->cgwb_refcnt to ->online_pin and always use it

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blkcg->cgwb_refcnt is used to delay blkcg offlining so that blkgs
don't get offlined while there are active cgwbs on them.  However, it
ends up making offlining unordered sometimes causing parents to be
offlined before children.

To fix it, we want child blkcgs to pin the parents' online states
turning the refcnt into a more generic online pinning mechanism.

In prepartion,

* blkcg->cgwb_refcnt -> blkcg->online_pin
* blkcg_cgwb_get/put() -> blkcg_pin/unpin_online()
* Take them out of CONFIG_CGROUP_WRITEBACK

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo
2019-07-24 10:37:22 -07:00
committed by Jens Axboe
parent 1a323ea535
commit d866dbf617
3 changed files with 19 additions and 32 deletions
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6
mm/backing-dev.c
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@@ -491,8 +491,8 @@ static void cgwb_release_workfn(struct work_struct *work)
css_put(wb->blkcg_css);
mutex_unlock(&wb->bdi->cgwb_release_mutex);
/* triggers blkg destruction if cgwb_refcnt becomes zero */
blkcg_cgwb_put(blkcg);
/* triggers blkg destruction if no online users left */
blkcg_unpin_online(blkcg);
fprop_local_destroy_percpu(&wb->memcg_completions);
percpu_ref_exit(&wb->refcnt);
@@ -592,7 +592,7 @@ static int cgwb_create(struct backing_dev_info *bdi,
list_add_tail_rcu(&wb->bdi_node, &bdi->wb_list);
list_add(&wb->memcg_node, memcg_cgwb_list);
list_add(&wb->blkcg_node, blkcg_cgwb_list);
blkcg_cgwb_get(blkcg);
blkcg_pin_online(blkcg);
css_get(memcg_css);
css_get(blkcg_css);
}