Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755767Ab0GMJsH (ORCPT ); Tue, 13 Jul 2010 05:48:07 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:35948 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755589Ab0GMJsB (ORCPT ); Tue, 13 Jul 2010 05:48:01 -0400 Date: Tue, 13 Jul 2010 10:46:12 +0100 From: Russell King - ARM Linux To: Mel Gorman Cc: 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, KAMEZAWA Hiroyuki Subject: Re: [RFC] Tight check of pfn_valid on sparsemem Message-ID: <20100713094612.GF20590@n2100.arm.linux.org.uk> References: <20100712155348.GA2815@barrios-desktop> <20100713093700.GD29885@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100713093700.GD29885@csn.ul.ie> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1188 Lines: 24 On Tue, Jul 13, 2010 at 10:37:00AM +0100, Mel Gorman wrote: > I prefer Kamezawa's suggestion of mapping on a ZERO_PAGE-like page full > of PageReserved struct pages because it would have better performance > and be more in line with maintaining the assumptions of the memory > model. If we go in this direction, I would strongly prefer it was an > ARM-only thing. As I've said, this is not possible without doing some serious page manipulation. Plus the pages that where there become unusable as they don't correspond with a PFN or obey phys_to_virt(). So there's absolutely no point to this. Now, why do we free the holes in the mem_map - because these holes can be extremely large. Every 512K of hole equates to one page of mem_map array. Balance that against memory placed at 0xc0000000 physical on some platforms, and with PHYSMEM_BITS at 32 and SECTION_SIZE_BITS at 19 - well, you do the maths. The result is certainly not pretty. -- 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/