From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751354AbdHaGzf (ORCPT ); Thu, 31 Aug 2017 02:55:35 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42320 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750790AbdHaGze (ORCPT ); Thu, 31 Aug 2017 02:55:34 -0400 Subject: Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure To: Laurent Dufour , Peter Zijlstra , Anshuman Khandual References: <1503007519-26777-1-git-send-email-ldufour@linux.vnet.ibm.com> <1503007519-26777-15-git-send-email-ldufour@linux.vnet.ibm.com> <20170827001823.n5wgkfq36z6snvf2@node.shutemov.name> <507e79d5-59df-c5b5-106d-970c9353d9bc@linux.vnet.ibm.com> <20170829120426.4ar56rbmiupbqmio@hirez.programming.kicks-ass.net> <848fa2c6-dbda-9a1e-2efd-3ce9b083365e@linux.vnet.ibm.com> <20170829134550.t7du5zdssvlzemtk@hirez.programming.kicks-ass.net> <20170830055800.GG32112@worktop.programming.kicks-ass.net> <12d54f18-6dec-5067-db87-d1a176d5160f@linux.vnet.ibm.com> Cc: "Kirill A. Shutemov" , paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org From: Anshuman Khandual Date: Thu, 31 Aug 2017 12:25:16 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <12d54f18-6dec-5067-db87-d1a176d5160f@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17083106-0044-0000-0000-000002845D11 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17083106-0045-0000-0000-00000717E2DE Message-Id: <0add5ad0-fd3d-efb7-f00c-7232dfc768af@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-31_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1708310105 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/30/2017 03:02 PM, Laurent Dufour wrote: > On 30/08/2017 07:58, Peter Zijlstra wrote: >> On Wed, Aug 30, 2017 at 10:33:50AM +0530, Anshuman Khandual wrote: >>> diff --git a/mm/filemap.c b/mm/filemap.c >>> index a497024..08f3042 100644 >>> --- a/mm/filemap.c >>> +++ b/mm/filemap.c >>> @@ -1181,6 +1181,18 @@ int __lock_page_killable(struct page *__page) >>> int __lock_page_or_retry(struct page *page, struct mm_struct *mm, >>> unsigned int flags) >>> { >>> + if (flags & FAULT_FLAG_SPECULATIVE) { >>> + if (flags & FAULT_FLAG_KILLABLE) { >>> + int ret; >>> + >>> + ret = __lock_page_killable(page); >>> + if (ret) >>> + return 0; >>> + } else >>> + __lock_page(page); >>> + return 1; >>> + } >>> + >>> if (flags & FAULT_FLAG_ALLOW_RETRY) { >>> /* >>> * CAUTION! In this case, mmap_sem is not released >> >> Yeah, that looks right. > > Hum, I'm wondering if FAULT_FLAG_RETRY_NOWAIT should be forced in the > speculative path in that case to match the semantics of > __lock_page_or_retry(). Doing that would force us to have another retry through classic fault path wasting all the work done till now through SPF. Hence it may be better to just wait, get the lock here and complete the fault. Peterz, would you agree ? Or we should do as suggested by Laurent. More over, forcing FAULT_FLAG_RETRY_NOWAIT on FAULT_FLAG_SPECULTIVE at this point would look like a hack.