linux-kernel - Re: [PATCHv9 1/3] rdmacg: Added rdma cgroup controller

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Date:	Sat, 12 Mar 2016 11:49:03 +0530
From:	Parav Pandit <pandit.parav@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	lizefan@...wei.com, Johannes Weiner <hannes@...xchg.org>,
	Doug Ledford <dledford@...hat.com>,
	Liran Liss <liranl@...lanox.com>,
	"Hefty, Sean" <sean.hefty@...el.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Haggai Eran <haggaie@...lanox.com>,
	Jonathan Corbet <corbet@....net>, james.l.morris@...cle.com,
	serge@...lyn.com, Or Gerlitz <ogerlitz@...lanox.com>,
	Matan Barak <matanb@...lanox.com>, akpm@...ux-foundation.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCHv9 1/3] rdmacg: Added rdma cgroup controller

Hi Tejun,

On Sat, Mar 5, 2016 at 10:50 PM, Parav Pandit <pandit.parav@...il.com> wrote:
> Hi Tejun,
>
> On Sat, Mar 5, 2016 at 6:22 PM, Tejun Heo <tj@...nel.org> wrote:
>> Hello, Parav.
>>
>> On Sat, Mar 05, 2016 at 04:45:09PM +0530, Parav Pandit wrote:
>>> Design that remains same from v6 to v10.
>>>   * spin lock is still fine grained at cgroup level instead of one
>>> global shared lock among all cgroups.
>>>      In future it can be optimized further to do per cpu or using
>>> single lock if required.
>>>   * file type enums are still present for max and current, as
>>> read/write call to those files is already taken care by common
>>> functions with required if/else.
>>>   * Resource limit setting is as it is, because number of devices are
>>> in range of 1 to 4 count in most use cases (as explained in
>>> documentation), and its not hot path.
>>
>> 1 and 2 are not okay.
> For (1) shall I have one spin lock that is uses across multiple
> hierarchy and multiple cgroup.
> Essentially one global lock among all cgroup. During hierarchical
> charging, continue to use same lock it at each level.
> Would that work in this first release?
>

I am waiting for your reply.
Shall one lock for all cgroup is ok with you?

> Can you please review the code for (2), I cannot think of any further
> helper functions that I can write.
> For both the file types, all the code is already common.
> file types are used only to find out whether to reference max variable
> or usage variable in structure.
> Which can also be made as array, but I do not want to lose the code
> readability for that little gain.
> What exactly is the issue in current implementation? You just
> mentioned that "its not good sign".
> Its readable, simple and serves the purpose, what am I missing?
>
If this is ok. I will keep the code as it is, because it uses common
helper functions for max and current files.


>> 3 is fine but resource [un]charging is not hot path?
> charge/uncharge is hot path from cgroup perspective.
> Considering 1 to 4 devices in system rpool list would grow upto 4
> entry deep at each cgroup level.
> I believe this is good enough to start with. O complexity wise its
> O(N). where N is number of devices in system.
>
>
>>
>> Thanks.
>>
>> --
>> tejun