From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757668Ab3A1Rvc (ORCPT ); Mon, 28 Jan 2013 12:51:32 -0500 Received: from fw-tnat.cambridge.arm.com ([217.140.96.21]:46998 "EHLO cam-smtp0.cambridge.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757602Ab3A1Rva (ORCPT ); Mon, 28 Jan 2013 12:51:30 -0500 Date: Mon, 28 Jan 2013 17:51:06 +0000 From: Will Deacon To: Joonsoo Kim Cc: Russell King , "js1304@gmail.com" , Nicolas Pitre , Catalin Marinas , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v3 0/3] introduce static_vm for ARM-specific static mapped area Message-ID: <20130128175106.GI23470@mudshark.cambridge.arm.com> References: <1358990934-4893-1-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1358990934-4893-1-git-send-email-iamjoonsoo.kim@lge.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, Jan 24, 2013 at 01:28:51AM +0000, Joonsoo Kim wrote: > In current implementation, we used ARM-specific flag, that is, > VM_ARM_STATIC_MAPPING, for distinguishing ARM specific static mapped area. > The purpose of static mapped area is to re-use static mapped area when > entire physical address range of the ioremap request can be covered > by this area. > > This implementation causes needless overhead for some cases. > For example, assume that there is only one static mapped area and > vmlist has 300 areas. Every time we call ioremap, we check 300 areas for > deciding whether it is matched or not. Moreover, even if there is > no static mapped area and vmlist has 300 areas, every time we call > ioremap, we check 300 areas in now. > > If we construct a extra list for static mapped area, we can eliminate > above mentioned overhead. > With a extra list, if there is one static mapped area, > we just check only one area and proceed next operation quickly. > > In fact, it is not a critical problem, because ioremap is not frequently > used. But reducing overhead is better idea. > > Another reason for doing this work is for removing vm_struct list management, > entirely. For more information, look at the following link. > http://lkml.org/lkml/2012/12/6/184 First patch looks good (removing the unused vmregion stuff) but I'm not so sure about the rest of it. If you really care about ioremap performance, perhaps it would be better to have a container struct around the vm_struct for static mappings and then stick them in an augmented rbtree so you can efficiently find the mapping encompassing a particular physical address? Will