Re: [PATCH v2 2/2] blk-cgroup: Optimize blkcg_rstat_flush()

[Waiman Long]

On 6/1/22 17:28, Tejun Heo wrote:
> On Wed, Jun 01, 2022 at 05:25:53PM -0400, Waiman Long wrote:
> > I think the best way to protect against blkg destruction is to get a percpu
> > reference when put into lockless list and put it back when removed.
> >
> > BTW, when I ran a test that continuously create and destroy containers, the
> > total number of blkcg's kept on increasing. There are some freeing of
> > blkcg's but no freeing of blkg's at all. Maybe we have a similar dying
> > blkcg's problem here. I will take a further look at that when I have time.
> They get pinned by per-cgroup writebacks which gets pinned by lingering page
> cache and other remaining accounted memory areas, so I think they can hang
> around if there's no memory pressure. But, yeah, it'd be great to verify
> that they actually go away under memory pressure.
>
> Thanks.
Thanks for the explanation. It makes sense to me.

Cheers,
Longman