On 09/07/2012 01:11 AM, Paul Turner wrote: > On Thu, Sep 6, 2012 at 1:46 PM, Tejun Heo <tj@xxxxxxxxxx> wrote: >> Hello, >> >> cc'ing Dhaval and Frederic. They were interested in the subject >> before and Dhaval was pretty vocal about cpuacct having a separate >> hierarchy (or at least granularity). > > Really? Time just has _not_ borne out this use-case. I'll let Dhaval > make a case for this but he should expect violent objection. > I strongly advise against physical violence. In case it is really necessary, please break his legs only. >> On Wed, Sep 05, 2012 at 12:04:47PM +0200, Peter Zijlstra wrote: >>>> cpuacct is rather unique tho. I think it's gonna be silly whether the >>>> hierarchy is unified or not. >>>> >>>> 1. If they always can live on the exact same hierarchy, there's no >>>> point in having the two separate. Just merge them. >>>> >>>> 2. If they need differing levels of granularity, they either need to >>>> do it completely separately as they do now or have some form of >>>> dynamic optimization if absolutely necesary. >>>> >>>> So, I think that choice is rather separate from other issues. If >>>> cpuacct is gonna be kept, I'd just keep it separate and warn that it >>>> incurs extra overhead for the current users if for nothing else. >>>> Otherwise, kill it or merge it into cpu. >>> >>> Quite, hence my 'proposal' to remove cpuacct. >>> >>> There was some whining last time Glauber proposed this, but the one >>> whining never convinced and has gone away from Linux, so lets just do >>> this. >>> >>> Lets make cpuacct print a deprecated msg to dmesg for a few releases and >>> make cpu do all this. >> >> I like it. Currently cpuacct is the only problematic one in this >> regard (cpuset to a much lesser extent) and it would be great to make >> it go away. >> >> Dhaval, Frederic, Paul, if you guys object, please voice your >> opinions. >> >>> The co-mounting stuff would have been nice for cpusets as well, knowing >>> all your tasks are affine to a subset of cpus allows for a few >>> optimizations (smaller cpumask iterations), but I guess we'll have to do >>> that dynamically, we'll just have to see how ugly that is. >> >> Forced co-mounting sounds rather silly to me. If the two are always >> gonna be co-mounted, why not just merge them and switch the >> functionality depending on configuration? I'm fairly sure the code >> would be simpler that way. > > It would be simpler but the problem is we'd break any userspace that > was just doing mount cpuacct? > > Further, even if it were mounting both, userspace code still has to be > changed to read from "cpu.export" instead of "cpuacct.export". > Only if we remove cpuacct. What we can do, and I thought about doing, is just merging cpuacct functionality into cpu. Then we move cpuacct to default no. It will be there for userspace if they absolutely want to use it. > I think a sane path on this front is: > > Immediately: > Don't allow cpuacct and cpu to be co-mounted on separate hierarchies > simultaneously. > that is precisely what my patch does, except it is a bit more generic. > That is: > mount none /dev/cgroup/cpuacct -t cgroupfs -o cpuacct : still works > mount none /dev/cgroup/cpu -t cgroupfs -o cpu : still works > mount none /dev/cgroup/cpux -t cgroupfs -o cpuacct,cpu : still works > > But the combination: > mount none /dev/cgroup/cpu -t cgroupfs -o cpu : still works > mount none /dev/cgroup/cpuacct -t cgroupfs -o cpu : EINVAL [or vice versa]. > > Also: > WARN_ON when mounting cpuacct without cpu, strongly explaining that > ANY such configuration is deprecated. > > Glauber's patchset goes most of the way towards enabling this. > yes. > In a release or two: > Make the restriction strict; don't allow individual mounting of > cpuacct, force it to be mounted ONLY with cpu. > > Glauber's patchset gives us this. > > Finally: > Mirror the interfaces to cpu, print nasty syslog messages about ANY > mounts of cpuacct > Follow that up by eventually removing cpuacct completely > Why don't start with mirroring? It gives more time for people to start switching to it. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>