Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753469Ab0LPXrH (ORCPT ); Thu, 16 Dec 2010 18:47:07 -0500 Received: from rcsinet10.oracle.com ([148.87.113.121]:30122 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751690Ab0LPXrE (ORCPT ); Thu, 16 Dec 2010 18:47:04 -0500 To: Hugh Dickins Cc: "Martin K. Petersen" , Ric Wheeler , Christian Brandt , linux-kernel@vger.kernel.org, Mike Snitzer Subject: Re: swap storage alignment and stride size From: "Martin K. Petersen" Organization: Oracle References: <4CFFBA7D.6060802@psi5.com> <4CFFE2EA.9040909@gmail.com> Date: Thu, 16 Dec 2010 18:46:41 -0500 In-Reply-To: (Hugh Dickins's message of "Wed, 15 Dec 2010 16:42:33 -0800 (PST)") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1201 Lines: 31 >>>>> "Hugh" == Hugh Dickins writes: >> You called it a "header page". Does that imply that it is page sized? Hugh> Yes. (Rather a nuisance on a PowerPC system which sometimes uses Hugh> a kernel with 4k pages and sometimes a kernel with 64k pages.) Ok. >> Or will it cause pages written to a 4k-aligned swap device to be >> misaligned? Hugh> No, the 4k-aligned remains 4k-aligned, of course. But if you Hugh> aligned your swap partition on, say, a 1MB boundary, and are Hugh> thinking of working in aligned 1MB blocks, then it may be awkward Hugh> that there's always this special 4k at the start (it could be Hugh> written back each time even though it hasn't changed, but it's Hugh> still an odd case). Yeah, I got that. I just wanted to make sure that the header was not 32 bytes or something like that because that would be highly painful from an I/O alignment perspective. -- Martin K. Petersen Oracle Linux Engineering -- 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/