Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755766Ab0GMUrM (ORCPT ); Tue, 13 Jul 2010 16:47:12 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:39299 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751908Ab0GMUrJ (ORCPT ); Tue, 13 Jul 2010 16:47:09 -0400 Subject: Re: [RFC] Tight check of pfn_valid on sparsemem From: Dave Hansen To: Russell King - ARM Linux Cc: KAMEZAWA Hiroyuki , Minchan Kim , Yinghai Lu , "H. Peter Anvin" , Andrew Morton , Shaohua Li , Yakui Zhao , linux-kernel@vger.kernel.org, linux-mm@kvack.org, arm-kernel@lists.infradead.org, kgene.kim@samsung.com, Mel Gorman In-Reply-To: <20100713183932.GB31162@n2100.arm.linux.org.uk> References: <20100712155348.GA2815@barrios-desktop> <20100713121947.612bd656.kamezawa.hiroyu@jp.fujitsu.com> <20100713132312.a7dfb100.kamezawa.hiroyu@jp.fujitsu.com> <20100713072009.GA19839@n2100.arm.linux.org.uk> <20100713163417.17895202.kamezawa.hiroyu@jp.fujitsu.com> <20100713165808.e340e6dc.kamezawa.hiroyu@jp.fujitsu.com> <20100713170222.9369e649.kamezawa.hiroyu@jp.fujitsu.com> <20100713183932.GB31162@n2100.arm.linux.org.uk> Content-Type: text/plain; charset="ANSI_X3.4-1968" Date: Tue, 13 Jul 2010 13:46:59 -0700 Message-ID: <1279054019.10995.18.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1216 Lines: 29 On Tue, 2010-07-13 at 19:39 +0100, Russell King - ARM Linux wrote: > On Tue, Jul 13, 2010 at 05:02:22PM +0900, KAMEZAWA Hiroyuki wrote: > > How about stop using SPARSEMEM ? What's the benefit ? It just eats up > > memory for mem_section[]. > > The problem with that approach is that sometimes the mem_map array > doesn't fit into any memory banks. > > We've gone around the loop of using flatmem with holes punched in it, > to using discontigmem, and now to using sparsemem. It seems none of > these solutions does what we need for ARM. I guess that's the price > we pay for not having memory architected to be at any particular place > in the physical memory map. What's the ARM hardware's maximum addressable memory these days? 4GB? A 4GB system would have 256 sections, which means 256*2*sizeof(unsigned long) for the mem_section[]. That's a pretty small amount of RAM. What sizes are the holes that are being punched these days? Smaller than 16MB? -- Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/