Re: [PATCH v2] memcg: Add memory.pressure_level events

[Minchan Kim <minchan@kernel.org>]

On Thu, Feb 21, 2013 at 10:55:52PM -0800, Anton Vorontsov wrote:
> On Fri, Feb 22, 2013 at 08:56:08AM +0900, Minchan Kim wrote:
> > [...] The my point is that you have a plan to support? Why I have a
> > question is that you said your goal is to replace lowmemory killer
> 
> In short: yes, of course, if the non-memcg interface will be in demand.
> 
> > but android don't have enabled CONFIG_MEMCG as you know well
> > so they should enable it for using just notifier? or they need another hack to
> > connect notifier to global thing?
> 
> A hack is not an option for me. :-) My final goal is to switch Android to
> use the notifier without need for hacks/external patches or
> drivers/staging.
> 
> But my current goal is to make the most generic case work, and do this in
> the most correct way. That is, vmpressure + MEMCG. Once I accomplish this,
> I can then think of any niche needs (such as Android).
> 
> There will be two possibilities for Android:
> 
> 1. Obviously, turn on CONFIG_MEMCG. We need to measure its effect on real
>    devices, and see if it makes sense. (Plus, maybe there are other uses
>    for MEMCG on Android?)

I'd like to see this one.

> 
> or
> 
> 2. Implement /sys/fs/cgroups/memory/memory.pressure_level interface
>    without MEMCG. Doing this will be really easy as we'll already have
>    vmpressure() core, and Android has CROUPS=y. But I do expect some
>    discussion like 'why don't you fix memcg instead?'. We'll have to
>    answer this question by looking back at '1.'

Of course.

> 
> Also note that cgroups vmpressure notifiers were tried by QEMU folks, and
> it seemed to be useful:
> 
>    http://lists.gnu.org/archive/html/qemu-devel/2012-12/msg02821.html 

I saw that.

> 
> So, nowadays it is not only about Android. Some time ago I also got an
> email from Orna Agmon Ben-Yehuda, who suggested to use vmpressure stuff
> with 'memcached' (but I didn't find time to actually try it, so far. :(
> Thanks for the email, btw!).

I also got received email from another people in embedded side about
memory notifier which I worked long time ago and I used to introduce
your work to them instead of my old solution.
It seems they don't use Android and has very small RAM so they want
to handle memory very efficiently. For such purpose, I hope vmpressure
become tiny and can support even NOMMU system.

> 
> So it is useful with or without MEMCG, and if we will really need to
> support vmpressure without MEMCG, I will have to implement the support in
> addition to MEMCG case, yes.

Thanks for your clarification.

> 
> Thanks,
> 
> Anton
> 
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-- 
Kind regards,
Minchan Kim

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