From mboxrd@z Thu Jan 1 00:00:00 1970 From: paulmck@linux.vnet.ibm.com (Paul E. McKenney) Date: Fri, 10 Jun 2011 11:47:38 -0700 Subject: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory Power Management In-Reply-To: <20110610180807.GB28500@srcf.ucam.org> References: <20110609185259.GA29287@linux.vnet.ibm.com> <20110610151121.GA2230@linux.vnet.ibm.com> <20110610155954.GA25774@srcf.ucam.org> <20110610165529.GC2230@linux.vnet.ibm.com> <20110610170535.GC25774@srcf.ucam.org> <20110610171939.GE2230@linux.vnet.ibm.com> <20110610172307.GA27630@srcf.ucam.org> <20110610175248.GF2230@linux.vnet.ibm.com> <20110610180807.GB28500@srcf.ucam.org> Message-ID: <20110610184738.GG2230@linux.vnet.ibm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Jun 10, 2011 at 07:08:07PM +0100, Matthew Garrett wrote: > On Fri, Jun 10, 2011 at 10:52:48AM -0700, Paul E. McKenney wrote: > > On Fri, Jun 10, 2011 at 06:23:07PM +0100, Matthew Garrett wrote: > > > I haven't seen too many ARM servers with 256GB of RAM :) I'm mostly > > > looking at this from an x86 perspective. > > > > But I have seen ARM embedded systems with CPU power consumption in > > the milliwatt range, which greatly reduces the amount of RAM required > > to get significant power savings from this approach. Three orders > > of magnitude less CPU power consumption translates (roughly) to three > > orders of magnitude less memory required -- and embedded devices with > > more than 256MB of memory are quite common. > > I'm not saying that powering down memory isn't a win, just that in the > server market we're not even getting unused memory into self refresh at > the moment. If we can gain that hardware capability then sub-node zoning > means that we can look at allocating (and migrating?) RAM in such a way > as to get a lot of the win that we'd gain from actually cutting the > power, without the added overhead of actually shrinking our working set. Agreed. And if I understand you correctly, then the patches that Ankita posted should help your self-refresh case, along with the originally intended the power-down case and special-purpose use of memory case. Thanx, Paul