Re: [PATCH v2 6/6] blkcg, memcg: make blkcg depend on memcg on the default hierarchy
From: Vivek Goyal
Date: Wed Jul 09 2014 - 07:58:39 EST
On Tue, Jul 08, 2014 at 05:53:51PM -0400, Tejun Heo wrote:
> Hello, Vivek.
> On Tue, Jul 08, 2014 at 03:42:26PM -0400, Vivek Goyal wrote:
> > I have couple questions about new semantics. Following is my
> > understanding. Is it right?
> > - So after this change one can not use blkio controller on unified
> > hiearchy if memory controller is mounted on some other hierarchy
> > and is not available for mounting unified hiearchy.
> Hmmm? No, the only behavior which changes is when both blkcg and
> memcg are mounted on the unified hierarchy. Nothing else changes.
> The dependency behavior kicks in iff memcg is available on the unified
Ok, good to know that dependency kicks in only if controlle being depended
on is available on the hierarchy.
> > - If blkio controller is enabled on unified hiearchy (memory controller
> > implicitly enabled), then one can't mount memory controller on other
> > hierarchies without first disabling blkio controller on unified hiearchy.
> Yes, blkio needs to be disabled to the root for memcg to be able to
> become free. This is an extra restriction but I don't think it's
> anything drastic. Once a controller starts being actively used on any
> hierarchy, nothing has been guaranteed about when the controller would
> become free again even if the whole hierarchy is reduced to the root.
Agreed. Thanks for the clarification.
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