From: Ingo Molnar <mingo@elte.hu>
To: Maxime Coquelin <maxime.coquelin@stericsson.com>
Cc: linux-mm@kvack.org, linaro-mm-sig@lists.linaro.org,
Mel Gorman <mel@csn.ul.ie>, Ankita Garg <ankita@in.ibm.com>,
linux-kernel@vger.kernel.org, linus.walleij@stericsson.com,
andrea.gallo@stericsson.com, vincent.guittot@stericsson.com,
philippe.langlais@stericsson.com, loic.pallardy@stericsson.com,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [RFCv1 0/6] PASR: Partial Array Self-Refresh Framework
Date: Mon, 30 Jan 2012 14:53:41 +0100 [thread overview]
Message-ID: <20120130135341.GA3720@elte.hu> (raw)
In-Reply-To: <1327930436-10263-1-git-send-email-maxime.coquelin@stericsson.com>
* Maxime Coquelin <maxime.coquelin@stericsson.com> wrote:
> The role of this framework is to stop the refresh of unused
> memory to enhance DDR power consumption.
I'm wondering in what scenarios this is useful, and how
consistently it is useful.
The primary concern I can see is that on most Linux systems with
an uptime more than a couple of minutes RAM gets used up by the
Linux page-cache:
$ uptime
14:46:39 up 11 days, 2:04, 19 users, load average: 0.11, 0.29, 0.80
$ free
total used free shared buffers cached
Mem: 12255096 12030152 224944 0 651560 6000452
-/+ buffers/cache: 5378140 6876956
Even mobile phones easily have days of uptime - quite often
weeks of uptime. I'd expect the page-cache to fill up RAM on
such systems.
So how will this actually end up saving power consistently? Does
it have to be combined with a VM policy that more aggressively
flushes cached pages from the page-cache?
A secondary concern is fragmentation: right now we fragment
memory rather significantly. For the Ux500 PASR driver you've
implemented the section size is 64 MB. Do I interpret the code
correctly in that a continuous, 64MB physical block of RAM has
to be 100% free for us to be able to turn off refresh and power
for this block of RAM?
Thanks,
Ingo
next prev parent reply other threads:[~2012-01-30 13:54 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-30 13:33 [RFCv1 0/6] PASR: Partial Array Self-Refresh Framework Maxime Coquelin
2012-01-30 13:33 ` [RFCv1 1/6] PASR: Initialize DDR layout Maxime Coquelin
2012-01-30 13:33 ` [RFCv1 2/6] PASR: Add core Framework Maxime Coquelin
2012-01-30 13:33 ` [RFCv1 3/6] PASR: mm: Integrate PASR in Buddy allocator Maxime Coquelin
2012-01-30 15:22 ` Mel Gorman
2012-01-30 16:52 ` Maxime Coquelin
2012-01-31 12:15 ` Maxime Coquelin
2012-01-31 14:01 ` Mel Gorman
2012-01-31 18:55 ` Maxime Coquelin
2012-02-03 11:44 ` Mel Gorman
2012-01-31 12:46 ` Pekka Enberg
2012-01-30 13:33 ` [RFCv1 4/6] PASR: Call PASR initialization Maxime Coquelin
2012-01-30 13:33 ` [RFCv1 5/6] PASR: Add Documentation Maxime Coquelin
2012-02-02 3:51 ` Randy Dunlap
2012-02-02 17:12 ` Maxime Coquelin
2012-01-30 13:33 ` [RFCv1 6/6] PASR: Ux500: Add PASR support Maxime Coquelin
2012-01-30 13:53 ` Ingo Molnar [this message]
2012-01-30 14:19 ` [RFCv1 0/6] PASR: Partial Array Self-Refresh Framework Maxime Coquelin
2012-01-31 12:39 ` Ingo Molnar
2012-01-31 14:48 ` Maxime Coquelin
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