From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757799AbYGAQgX (ORCPT ); Tue, 1 Jul 2008 12:36:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751207AbYGAQgO (ORCPT ); Tue, 1 Jul 2008 12:36:14 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:56721 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751185AbYGAQgM (ORCPT ); Tue, 1 Jul 2008 12:36:12 -0400 Date: Tue, 1 Jul 2008 09:35:34 -0700 (PDT) From: Linus Torvalds To: Paul Mundt cc: Hideo Saito , linux-sh@vger.kernel.org, Linux Kernel Mailing List Subject: Re: follow_page() performance regressions In-Reply-To: Message-ID: References: <20080701.132439.68562265.saito@densan.co.jp> <20080701052543.GA4726@linux-sh.org> User-Agent: Alpine 1.10 (LFD 962 2008-03-14) 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 On Tue, 1 Jul 2008, Linus Torvalds wrote: > > - some cache issue on SH. ZERO_PAGE is a single page at a fixed virtual > address, while it used to populate the page tables with individual > pages. Normally, this should be *better* for caching, but maybe there > is some conflict? What kind of caches does SH have (virtually indexed?) Actually, this one is unlikely. ZERO_PAGE _used_ to be problematic on some virtually indexed caches, because the same physical page would get mapped into multiple places virtually, which in turn then caused some cache or TLB conflict or something (I forget - MIPS was the main offender). But because we now use just the single kernel virtual address for accessing the ZERO_PAGE, that really shouldn't matter. Unless the particular user of follow_pages() that triggers in this case is doing something odd, of course. Linus