From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3F5E7C04ABB for ; Tue, 11 Sep 2018 12:12:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0229E20833 for ; Tue, 11 Sep 2018 12:12:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0229E20833 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727751AbeIKRL2 (ORCPT ); Tue, 11 Sep 2018 13:11:28 -0400 Received: from mx2.suse.de ([195.135.220.15]:60896 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726678AbeIKRL1 (ORCPT ); Tue, 11 Sep 2018 13:11:27 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 16E5FAFC3; Tue, 11 Sep 2018 12:12:23 +0000 (UTC) Date: Tue, 11 Sep 2018 14:12:22 +0200 From: Joerg Roedel To: Meelis Roos Cc: Thomas Gleixner , Linux Kernel list , linux-mm@kvack.org, Andrea Arcangeli , Linus Torvalds Subject: Re: 32-bit PTI with THP = userspace corruption Message-ID: <20180911121128.ikwptix6e4slvpt2@suse.de> References: <20180830205527.dmemjwxfbwvkdzk2@suse.de> <20180831070722.wnulbbmillxkw7ke@suse.de> <20180911114927.gikd3uf3otxn2ekq@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170421 (1.8.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 11, 2018 at 02:58:10PM +0300, Meelis Roos wrote: > The machines where I have PAE off are the ones that have less memory. > PAE is off just for performance reasons, not lack of PAE. PAE should be > present on all of my affected machines anyway and current distributions > seem to mostly assume 686 and PAE anyway for 32-bit systems. Right, most distributions don't even provide a non-PAE kernel for their users anymore. How big is the performance impact of using PAE over legacy paging? It shouldn't be too big because the top-level of the page-table only has 4 entries and is completly cached in the CPU. This makes %cr3 switches slower, but the page-walk itself still only needs 2 memory accesses. The page-table entries are also 8 bytes instead of 4 bytes, so that there is less locality in page-walks and probably a higher cache-miss rate. Regards, Joerg