[systemd-devel] [PATCH v2] cgroup-util: fix is_valid check to pass for unified cgroup hierchy.

[Dimitri John Ledkov]

On 1 June 2015 at 09:03, Umut Tezduyar Lindskog <umut at tezduyar.com> wrote:
> On Fri, May 29, 2015 at 12:25 PM, Lennart Poettering
> <lennart at poettering.net> wrote:
>> On Fri, 29.05.15 00:24, Dimitri John Ledkov (dimitri.j.ledkov at intel.com) wrote:
>>
>>> On 28 May 2015 at 18:08, Lennart Poettering <lennart at poettering.net> wrote:
>>> > On Thu, 28.05.15 16:42, Dimitri John Ledkov (dimitri.j.ledkov at intel.com) wrote:
>>> >
>>> >> It appears in /proc/self/cgroup as `0::/'
>>> >
>>> > What precisely does this fix?
>>> >
>>> > I mean, we need to do some major rework of things before the unified
>>> > hierarchy is really supported in systemd, and this one thing won't
>>> > really get us too much in this regard, does it?
>>> >
>>>
>>> I'm starting to explore possibilities to start work towards supporting
>>> unified cgroups hierarchy, or at least be able to boot with it. I'll
>>> send a larger patch series in one go later than with all the bits that
>>> offer something more tangible, albeit disabled by default behind
>>> configure options (like kdbus) given that unified hierarchy is still
>>> marked experimental in the kernel.
>>
>> Ah, it's actually my big thing to work on for the next weeks too...
>
> What is the advantage of having a unified hierarchy, could you guys explain?

There are a few. Read more in the linux documentation:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/cgroups/unified-hierarchy.txt

For me, I'm spending a lot of time during boot forking cgroups release
agent user-space binary, which establishes IPC connection to systemd
to notify that a cgroup was released. And essentially oneshot services
during boot pay sequential price of executing two processes rather
than just one. Hence exposure of cgroups.populated field is very
desirable for me. Currently only available on the unified hierarchy,
but I'm not sure why it couldn't be enabled on the old one, given that
it is forward compatible.

-- 
Regards,

Dimitri.
Pura Vida!

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