From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 26 May 2008 10:23:09 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 0/3] explicitly document overloaded page flags V2 Message-Id: <20080526102309.01b9bc9a.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andy Whitcroft Cc: linux-mm@kvack.org, Andrew Morton , Christoph Lameter , KOSAKI Motohiro , Rik van Riel , Jeremy Fitzhardinge , linux-kernel@vger.kernel.org List-ID: On Fri, 23 May 2008 17:33:01 +0100 Andy Whitcroft wrote: > With the recent page flag reorganisation we have a single enum which > defines the valid page flags and their values, nice and clear. However > there are a number of bits which are overloaded by different subsystems. > Firstly there is PG_owner_priv_1 which is used by filesystems and by XEN. > Secondly both SLOB and SLUB use a couple of extra page bits to manage > internal state for pages they own; both overlay other bits. All of these > "aliases" are scattered about the source making it very hard for a reader > to know if the bits are safe to rely on in all contexts; confusion here > is bad. > > As we now have a single place where the bits are clearly assigned it makes > sense to clarify the reuse of bits by making the aliases explicit and > visible with the original bit assignments. This patch creates explicit > aliases within the enum itself for the overloaded bits, creates standard > bit accessors PageFoo etc. and uses those throughout. > > This version pulls the bit manipulation out to standard named page bit > accessors as suggested by Christoph, it retains the explicit mapping to > the overlayed bits. A fusion of both ideas. This has been SLUB and > SLOB have been compile tested on x86_64 only, and SLUB boot tested. > If people feel this is worth doing then I can run a fuller set of testing. > Thanks, I like this style of page-flags definition. BTW, I have a quiestion as crash-dump user. With this 'enum' style, position of each flags in page->flags depends on configs. Can we know what a bit means from dump or bad_page()'s message ? (not a big problem now but..) Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org