Re: [PATCH 11/11] blkcg: implement per-blkg request allocation

Tejun Heo
2012-04-27T15:02:25Z

Hello,

On Fri, Apr 27, 2012 at 10:54:01AM -0400, Jeff Moyer wrote:
> > This patch implements per-blkg request_list. Each blkg has its own
> > request_list and any IO allocates its request from the matching blkg
> > making blkcgs completely isolated in terms of request allocation.
>
> So, nr_requests is now actually nr_requests * # of blk cgroups. Is that
> right? Are you at all concerned about the amount of memory that can be
> tied up as the number of cgroups increases?

Yeah, I thought about it and I don't think there's a single good
solution here. The other extreme would be splitting nr_requests by
the number of cgroups but that seems even worse - each cgroup should
be able to hit maximum throughput. Given that a lot of workloads tend
to regulate themselves before hitting nr_requests, I think it's best
to leave it as-is and treat each cgroup as having separate channel for
now. It's a configurable parameter after all.

Thanks.

--
tejun