From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753312Ab1GHBd1 (ORCPT ); Thu, 7 Jul 2011 21:33:27 -0400 Received: from mail.lang.hm ([64.81.33.126]:36564 "EHLO bifrost.lang.hm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752658Ab1GHBd0 (ORCPT ); Thu, 7 Jul 2011 21:33:26 -0400 Date: Thu, 7 Jul 2011 18:32:17 -0700 (PDT) From: david@lang.hm X-X-Sender: dlang@asgard.lang.hm To: Pekka Enberg cc: Ankita Garg , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-pm@lists.linux-foundation.org, svaidy@linux.vnet.ibm.com, thomas.abraham@linaro.org, Dave Hansen , "Paul E. McKenney" , KAMEZAWA Hiroyuki , Matthew Garrett , Arjan van de Ven , Christoph Lameter Subject: Re: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory Power Management In-Reply-To: Message-ID: References: <1306499498-14263-1-git-send-email-ankita@in.ibm.com> <20110629130038.GA7909@in.ibm.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 7 Jul 2011, Pekka Enberg wrote: > On Wed, 6 Jul 2011, Pekka Enberg wrote: >>> Why does the allocator need to know about address boundaries? Why >>> isn't it enough to make the page allocator and reclaim policies favor >>> using >>> memory from lower addresses as aggressively as possible? That'd mean >>> we'd favor the first memory banks and could keep the remaining ones >>> powered off as much as possible. >>> >>> IOW, why do we need to support scenarios such as this: >>> >>> bank 0 bank 1 bank 2 bank3 >>> | online | offline | online | offline | >> > On Wed, 6 Jul 2011, david@lang.hm wrote: >> I believe that there are memory allocations that cannot be moved after they >> are made (think about regions allocated to DMA from hardware where the >> hardware has already been given the address space to DMA into) >> >> As a result, you may not be able to take bank 2 offline, so your option is >> to either leave banks 0-2 all online, or support emptying bank 1 and taking >> it offline. > > But drivers allocate DMA memory for hardware during module load and stay > pinned there until the driver is unloaded, no? So in practice DMA buffers are > going to be in banks 0-1? that depends on when the device was initialized. it is common for them to be in the beginning, but with hotplug, who knows. David Lang