From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751386AbdKHIao (ORCPT ); Wed, 8 Nov 2017 03:30:44 -0500 Received: from mail-wm0-f42.google.com ([74.125.82.42]:56854 "EHLO mail-wm0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751055AbdKHIal (ORCPT ); Wed, 8 Nov 2017 03:30:41 -0500 X-Google-Smtp-Source: ABhQp+SSnT/+cPA0IajC5+khMqePtSCzz6H1SEHs9gckG1ZvCitLm4Eu+EIbsAjGbOa+VE/BTfBMrA== Date: Wed, 8 Nov 2017 11:30:38 +0300 From: "Kirill A. Shutemov" To: Michael Ellerman Cc: "Aneesh Kumar K.V" , Nicholas Piggin , Florian Weimer , linux-arch@vger.kernel.org, Dave Hansen , Peter Zijlstra , Linus Torvalds , Ingo Molnar , Linux Kernel Mailing List , Andy Lutomirski , linux-mm , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Thomas Gleixner , "Kirill A. Shutemov" Subject: Re: POWER: Unexpected fault when writing to brk-allocated memory Message-ID: <20171108083038.djj3qdhhnrazkk7b@node.shutemov.name> References: <20171106192524.12ea3187@roar.ozlabs.ibm.com> <546d4155-5b7c-6dba-b642-29c103e336bc@redhat.com> <20171107160705.059e0c2b@roar.ozlabs.ibm.com> <20171107111543.ep57evfxxbwwlhdh@node.shutemov.name> <20171107222228.0c8a50ff@roar.ozlabs.ibm.com> <20171107122825.posamr2dmzlzvs2p@node.shutemov.name> <20171108002448.6799462e@roar.ozlabs.ibm.com> <2ce0a91c-985c-aad8-abfa-e91bc088bb3e@linux.vnet.ibm.com> <87y3nh2wt5.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87y3nh2wt5.fsf@concordia.ellerman.id.au> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 08, 2017 at 03:56:06PM +1100, Michael Ellerman wrote: > "Aneesh Kumar K.V" writes: > > >> > >> If it is decided to keep these kind of heuristics, can we get just a > >> small but reasonably precise description of each change to the > >> interface and ways for using the new functionality, such that would be > >> suitable for the man page? I couldn't fix powerpc because nothing > >> matches and even Aneesh and you differ on some details (MAP_FIXED > >> behaviour). > > > > > > I would consider MAP_FIXED as my mistake. We never discussed this > > explicitly and I kind of assumed it to behave the same way. ie, we > > search in lower address space (128TB) if the hint addr is below 128TB. > > > > IIUC we agree on the below. > > > > 1) MAP_FIXED allow the addr to be used, even if hint addr is below 128TB > > but hint_addr + len is > 128TB. > > So: > mmap(0x7ffffffff000, 0x2000, ..., MAP_FIXED ...) = 0x7ffffffff000 > > > 2) For everything else we search in < 128TB space if hint addr is below > > 128TB > > mmap((x < 128T), 0x1000, ...) = (y < 128T) > ... > mmap(0x7ffffffff000, 0x1000, ...) = 0x7ffffffff000 > mmap(0x800000000000, 0x1000, ...) = 0x800000000000 > ... > mmap((x >= 128T), 0x1000, ...) = (y >= 128T) > > > 3) We don't switch to large address space if hint_addr + len > 128TB. > > The decision to switch to large address space is primarily based on hint > > addr > > But does the mmap succeed in that case or not? > > ie: mmap(0x7ffffffff000, 0x2000, ...) = ? It does, but resulting address doesn't match the hint. It's somewhere below 47-bit border. -- Kirill A. Shutemov