Messages in this thread | | | Date | Mon, 15 Nov 2010 19:38:19 +0100 | From | Jens Axboe <> | Subject | Re: [RFC] blk-cgroup: Allow creation of hierarchical cgroups |
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On 2010-11-15 16:28, Vivek Goyal wrote: > On Tue, Nov 02, 2010 at 06:20:30PM -0400, Vivek Goyal wrote: >> o Allow hierarchical cgroup creation for blkio controller >> >> o Currently we disallow it as both the io controller policies (throttling >> as well as proportion bandwidth) do not support hierarhical accounting >> and control. But the flip side is that blkio controller can not be used with >> libvirt as libvirt creates a cgroup hierarchy deeper than 1 level. >> >> <top-level-cgroup-dir>/<controller>/libvirt/qemu/<virtual-machine-groups> >> >> o So this patch will allow creation of cgroup hierarhcy but at the backend >> everything will be treated as flat. So if somebody created a an hierarchy >> like as follows. >> >> root >> / \ >> test1 test2 >> | >> test3 >> >> CFQ and throttling will practically treat all groups at same level. >> >> pivot >> / | \ \ >> root test1 test2 test3 >> >> o Once we have actual support for hierarchical accounting and control >> then we can introduce another cgroup tunable file "blkio.use_hierarchy" >> which will be 0 by default but if user wants to enforce hierarhical >> control then it can be set to 1. This way there should not be any >> ABI problems down the line. >> >> o The only not so pretty part is introduction of extra file "use_hierarchy" >> down the line. Kame-san had mentioned that hierarhical accounting is >> expensive in memory controller hence they keep it off by default. I >> suspect same will be the case for IO controller also as for each IO >> completion we shall have to account IO through hierarchy up to the root.. >> if yes, then it probably is not a very bad idea to introduce this extra >> file so that it will be used only when somebody needs it and some people >> might enable hierarchy only in part of the hierarchy. >> >> o This is how basically memory controller also uses "use_hierarhcy" and >> they also allowed creation of hierarchies when actual backend support >> was not available. >> >> Signed-off-by: Vivek Goyal <vgoyal@redhat.com> >> --- > > Hi Jens, > > Do you have any concerns about this patch? If not, can you please apply > it.
Applied to for-2.6.38/rc2-holder, it'll be merged into for-2.6.38/core once -rc2 has been tagged (and I can pull in the conflicting bits).
-- Jens Axboe
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