Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756035AbZDWIPF (ORCPT ); Thu, 23 Apr 2009 04:15:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754360AbZDWIOm (ORCPT ); Thu, 23 Apr 2009 04:14:42 -0400 Received: from systemlinux.org ([83.151.29.59]:45981 "EHLO m18s25.vlinux.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752252AbZDWIOk (ORCPT ); Thu, 23 Apr 2009 04:14:40 -0400 Date: Thu, 23 Apr 2009 10:07:29 +0200 From: Andre Noll To: "H. Peter Anvin" Cc: Bill Davidsen , Matti Aarnio , Jesper Juhl , Prakash Punnoor , Michael Tokarev , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, neilb@suse.de Subject: Re: Proposal: make RAID6 code optional Message-ID: <20090423080729.GA11504@skl-net.de> References: <49E98AD2.8060601@msgid.tls.msk.ru> <200904181117.03418.prakash@punnoor.de> <20090418145850.GD28512@mea-ext.zmailer.org> <49EDD11E.2030309@tmr.com> <49EE00F9.6090000@zytor.com> <20090422180051.GD13280@skl-net.de> <49EF6457.90505@zytor.com> <20090422185703.GF13280@skl-net.de> <49EFC5DD.9090201@zytor.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="wRRV7LY7NUeQGEoC" Content-Disposition: inline In-Reply-To: <49EFC5DD.9090201@zytor.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1999 Lines: 58 --wRRV7LY7NUeQGEoC Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 18:35, H. Peter Anvin wrote: > Andre Noll wrote: > > On 11:39, H. Peter Anvin wrote: > >> Yes, I believe it would be easier than having dynamically allocated=20 > >> arrays. Dynamically generated arrays using static memory allocations= =20 > >> (bss) is one thing, but that would only reduce size of the module on= =20 > >> disk, which I don't think anyone considers a problem. > >=20 > > We would save 64K of RAM in the raid5-only case if we'd defer the > > allocation of the multiplication table until the first raid6 array > > is about to be started. >=20 > Yes, and we'd have to access it through a pointer for the rest of eternit= y. True. You put a lot of effort into raid6 to make it fast, so you know best how much that would slow down the code. If using a pointer instead of an array would have a measurable impact on the raid6 performance, then we should indeed avoid using dynamically allocated memory for the table. As this slowdown likely depends on the arch, it is not easy to measure. So I guess the best way to decrease memory usage for the raid5-only case is to put the raid6-specific code into a separate module as you suggested earlier. Thanks Andre --=20 The only person who always got his work done by Friday was Robinson Crusoe --wRRV7LY7NUeQGEoC Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (GNU/Linux) iD8DBQFJ8CHBWto1QDEAkw8RAu7BAJwPq5oS8Z30I26UNivvzOx8bEF/xwCfcY2W Rvh5eT1BTEipBSoeT95Tsoo= =6VR5 -----END PGP SIGNATURE----- --wRRV7LY7NUeQGEoC-- -- 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/