From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f176.google.com (mail-wi0-f176.google.com [209.85.212.176]) by kanga.kvack.org (Postfix) with ESMTP id 926986B0032 for ; Sun, 28 Dec 2014 07:51:44 -0500 (EST) Received: by mail-wi0-f176.google.com with SMTP id ex7so20099480wid.3 for ; Sun, 28 Dec 2014 04:51:44 -0800 (PST) Received: from mout.kundenserver.de (mout.kundenserver.de. [212.227.17.10]) by mx.google.com with ESMTPS id fz7si66628742wjb.100.2014.12.28.04.51.43 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Dec 2014 04:51:43 -0800 (PST) From: Arnd Bergmann Subject: Re: [RFC][PATCH RESEND] mm: vmalloc: remove ioremap align constraint Date: Tue, 23 Dec 2014 21:58:49 +0100 Message-ID: <11656044.WGcPr1b8t8@wuerfel> In-Reply-To: <1419328813-2211-1-git-send-email-d.safonov@partner.samsung.com> References: <1419328813-2211-1-git-send-email-d.safonov@partner.samsung.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: owner-linux-mm@kvack.org List-ID: To: linux-arm-kernel@lists.infradead.org Cc: Dmitry Safonov , linux-mm@kvack.org, Nicolas Pitre , Russell King , Dyasly Sergey , Will Deacon , linux-kernel@vger.kernel.org, James Bottomley , Arnd Bergmann , Guan Xuetao , Andrew Morton On Tuesday 23 December 2014 13:00:13 Dmitry Safonov wrote: > ioremap uses __get_vm_area_node which sets alignment to fls of requested size. > I couldn't find any reason for such big align. Does it decrease TLB misses? > I tested it on custom ARM board with 200+ Mb of ioremap and it works. > What am I missing? The alignment was originally introduced in this commit: commit ff0daca525dde796382b9ccd563f169df2571211 Author: Russell King Date: Thu Jun 29 20:17:15 2006 +0100 [ARM] Add section support to ioremap Allow section mappings to be setup using ioremap() and torn down with iounmap(). This requires additional support in the MM context switch to ensure that mappings are properly synchronised when mapped in. Based an original implementation by Deepak Saxena, reworked and ARMv6 support added by rmk. Signed-off-by: Russell King and then later extended to 16MB supersection mappings, which indeed is used to reduce TLB pressure. I don't see any downsides to it, why change it? Arnd -- 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