Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751430Ab0BHMLF (ORCPT ); Mon, 8 Feb 2010 07:11:05 -0500 Received: from gir.skynet.ie ([193.1.99.77]:46956 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750984Ab0BHMLD (ORCPT ); Mon, 8 Feb 2010 07:11:03 -0500 Date: Mon, 8 Feb 2010 12:10:48 +0000 From: Mel Gorman To: David Rientjes Cc: Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 2/7] Export unusable free space index via /proc/pagetypeinfo Message-ID: <20100208121048.GB23680@csn.ul.ie> References: <1262795169-9095-1-git-send-email-mel@csn.ul.ie> <1262795169-9095-3-git-send-email-mel@csn.ul.ie> <20100205102349.GB20412@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2115 Lines: 47 On Fri, Feb 05, 2010 at 01:40:21PM -0800, David Rientjes wrote: > On Fri, 5 Feb 2010, Mel Gorman wrote: > > > > > + /* > > > > + * Index should be a value between 0 and 1. Return a value to 3 > > > > + * decimal places. > > > > + * > > > > + * 0 => no fragmentation > > > > + * 1 => high fragmentation > > > > + */ > > > > + return ((info->free_pages - (info->free_blocks_suitable << order)) * 1000) / info->free_pages; > > > > + > > > > > > This value is only for userspace consumption via /proc/pagetypeinfo, so > > > I'm wondering why it needs to be exported as an index. Other than a loss > > > of precision, wouldn't this be easier to understand (especially when > > > coupled with the free page counts already exported) if it were multipled > > > by 100 rather than 1000 and shown as a percent of _usable_ free memory at > > > each order? > > > > I find it easier to understand either way, but that's hardly a surprise. > > The 1000 is because of the loss of precision. I can make it a 100 but I > > don't think it makes much of a difference. > > > > This suggestion was coupled with the subsequent note that there is no > documentation of what "unusuable free space index" is, except by the > implementation itself. Since the value isn't used by the kernel, I think > exporting the value as a percent would be easier understood by the user > without looking up the semantics. I don't have strong feelings either > way, however. > I'm writing documentation. I'm keeping with the 1000 value because a) I like the precision and b) the fragmentation index is not related to percentages and I think having one as a percentage and the other as an index would cause confusion. Thanks -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/