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

[Tejun Heo <tj@xxxxxxxxxx>]

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
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