linux-kernel - Re: [RFC 1/3] /dev/low_mem

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Date:	Tue, 17 Jan 2012 21:49:13 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Minchan Kim <minchan@...nel.org>, linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, leonid.moiseichuk@...ia.com,
	kamezawa.hiroyu@...fujitsu.com, mel@....ul.ie, rientjes@...gle.com,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ronen Hod <rhod@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [RFC 1/3] /dev/low_mem_notify

On Tue, Jan 17, 2012 at 9:30 PM, Rik van Riel <riel@...hat.com> wrote:
> Looks like a nice extensible interface to me.
>
> The only thing is, I expect we will not want to wake
> up processes most of the time, when there is no memory
> pressure, because that would just waste battery power
> and/or cpu time that could be used for something else.
>
> The desire to avoid such wakeups makes it harder to
> wake up processes at arbitrary points set by the API.

Sure. You could either bump up the threshold or use Minchan's hooks - or both.

On Tue, Jan 17, 2012 at 9:30 PM, Rik van Riel <riel@...hat.com> wrote:
> Another issue is that we might be running two programs
> on the system, each with a different threshold for
> "lets free some of my cache".  Say one program sets
> the threshold at 20% free/cache memory, the other
> program at 10%.
>
> We could end up with the first process continually
> throwing away its caches, while the second process
> never gives its unused memory back to the kernel.
>
> I am not sure what the right thing to do would be...

One option is to use per-process thresholds on RSS, for example, and
also support system-wide thresholds.

That said, I'd really like to see the N9 and Android policies
supported with this ABI. It's much easier to make it generic once we
support real-world use cases.

                        Pekka
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