From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964873AbdKGNqO (ORCPT ); Tue, 7 Nov 2017 08:46:14 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:52486 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753714AbdKGNqN (ORCPT ); Tue, 7 Nov 2017 08:46:13 -0500 Subject: Re: POWER: Unexpected fault when writing to brk-allocated memory To: Nicholas Piggin , "Kirill A. Shutemov" Cc: Florian Weimer , "Kirill A. Shutemov" , linuxppc-dev@lists.ozlabs.org, linux-mm , Andrew Morton , Andy Lutomirski , Dave Hansen , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , linux-arch@vger.kernel.org, Ingo Molnar , Linux Kernel Mailing List References: <20171105231850.5e313e46@roar.ozlabs.ibm.com> <871slcszfl.fsf@linux.vnet.ibm.com> <20171106174707.19f6c495@roar.ozlabs.ibm.com> <24b93038-76f7-33df-d02e-facb0ce61cd2@redhat.com> <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> From: "Aneesh Kumar K.V" Date: Tue, 7 Nov 2017 19:15:58 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171108002448.6799462e@roar.ozlabs.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 17110713-0056-0000-0000-000003E59458 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008026; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000239; SDB=6.00942439; UDB=6.00475402; IPR=6.00722727; BA=6.00005676; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017895; XFM=3.00000015; UTC=2017-11-07 13:46:09 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17110713-0057-0000-0000-0000081CAC60 Message-Id: <2ce0a91c-985c-aad8-abfa-e91bc088bb3e@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-11-07_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1711070189 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > 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. 2) For everything else we search in < 128TB space if hint addr is below 128TB 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 Is there any other rule we need to outline? Or is any of the above not correct? -aneesh