Messages in this thread | | | Date | Fri, 11 May 2007 08:01:30 +0530 | From | Balbir Singh <> | Subject | Re: [ckrm-tech] [PATCH 3/9] Containers (V9): Add tasks file interface |
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Paul Menage wrote: > On 5/8/07, Balbir Singh <balbir@linux.vnet.ibm.com> wrote: >> >> I now have a use case for maintaining a per-container task list. >> I am trying to build a per-container stats similar to taskstats. >> I intend to support container accounting of >> >> 1. Tasks running >> 2. Tasks stopped >> 3. Tasks un-interruptible >> 4. Tasks blocked on IO >> 5. Tasks sleeping >> >> This would provide statistics similar to the patch that Pavel had sent >> out. >> >> I faced the following problems while trying to implement this feature >> >> 1. There is no easy way to get a list of all tasks belonging to a >> container >> (we need to walk all threads) > > Well, walking the taks list is pretty easy - but yes, it could become > inefficient when there are many small containers in use. > > I've got some ideas for a way of tracking this specifically for > containers with subsystems that want this, while avoiding the overhead > for subsystems that don't really need it. I'll try to add them to the > next patchset.
Super!
> >> 2. There is no concept of a container identifier. When a user issues a >> command >> to extract statistics, the only unique container identifier is the >> container >> path, which means that we need to do a path lookup to determine the >> dentry >> for the container (which gets quite ugly with all the string >> manipulation) > > We could just cache the container path permanently in the container, > and invalidate it if any of its parents gets renamed. (I imagine this > happens almost never.) >
Here's what I have so far, I cache the mount point of the container and add the container path to it. I'm now stuck examining tasks, while walking through a bunch of tasks, there is no easy way of knowing the container path of the task without walking all subsystems and then extracting the containers absolute path.
>> >> Adding a container id, will make it easier to find a container and >> return >> statistics belonging to the container. > > Not unreasonable, but there are a few questions that would have to be > answered: > > - how is the container id picked? Like a pid, or user-defined? Or some > kind of string? >
I was planning on using a hierarchical scheme, top 8 bits for the container hierarchy and bottom 24 for a unique id. The id is automatically selected. Once we know the container id, we'll need a more efficient mechanism to map the id to the container.
> - how would it be exposed to userspace? A generic control file > provided by the container filesystem in all container directories? >
A file in all container directories is an option
> - can you give a more concrete example of how this would actually be > useful? For your container stats, it seems that just reading a control > file in the container's directory would give you the stats that you > want, and userspace already knows the container's name/id since it > opened the control file. >
Sure, the plan is to build a containerstats interface like taskstats. In taskstats, we exchange data between user space and kernel space using genetlink sockets. We have a push and pull mechanism for statistics.
> Paul
-- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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