Re: [PATCH v1 3/3] mm: per-process reclaim

[Vinayak Menon <vinmenon@codeaurora.org>]

On 6/17/2016 12:54 PM, Balbir Singh wrote:
>
> On 14/06/16 01:06, Johannes Weiner wrote:
>> Hi Minchan,
>>
>> On Mon, Jun 13, 2016 at 04:50:58PM +0900, Minchan Kim wrote:
>>> These day, there are many platforms available in the embedded market
>>> and sometime, they has more hints about workingset than kernel so
>>> they want to involve memory management more heavily like android's
>>> lowmemory killer and ashmem or user-daemon with lowmemory notifier.
>>>
>>> This patch adds add new method for userspace to manage memory
>>> efficiently via knob "/proc/<pid>/reclaim" so platform can reclaim
>>> any process anytime.
>> Cgroups are our canonical way to control system resources on a per
>> process or group-of-processes level. I don't like the idea of adding
>> ad-hoc interfaces for single-use cases like this.
>>
>> For this particular case, you can already stick each app into its own
>> cgroup and use memory.force_empty to target-reclaim them.
>>
>> Or better yet, set the soft limits / memory.low to guide physical
>> memory pressure, once it actually occurs, toward the least-important
>> apps? We usually prefer doing work on-demand rather than proactively.
>>
>> The one-cgroup-per-app model would give Android much more control and
>> would also remove a *lot* of overhead during task switches, see this:
>> https://lkml.org/lkml/2014/12/19/358
> Yes, I'd agree. cgroups can group many tasks, but the group size can be
> 1 as well. Could you try the same test with the recommended approach and
> see if it works as desired? 
>
With cgroup v2, IIUC there can be only a single hierarchy where all controllers exist, and
a process can be part of only one cgroup. If that is true, with per task cgroup, a task can
be present only in its own cgroup. That being the case would it be feasible to have other
parallel controllers like CPU which would not be able to work efficiently with per task cgroup ?