From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751436AbeEVLrY (ORCPT ); Tue, 22 May 2018 07:47:24 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:48686 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751236AbeEVLrX (ORCPT ); Tue, 22 May 2018 07:47:23 -0400 Subject: Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT To: Randy Dunlap , akpm@linux-foundation.org, mhocko@kernel.org, peterz@infradead.org, kirill@shutemov.name, ak@linux.intel.com, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , sergey.senozhatsky.work@gmail.com, Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, Daniel Jordan , David Rientjes , Jerome Glisse , Ganesh Mahendran , Minchan Kim , Punit Agrawal , vinayak menon , Yang Shi Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, paulmck@linux.vnet.ibm.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org References: <1526555193-7242-1-git-send-email-ldufour@linux.vnet.ibm.com> <1526555193-7242-2-git-send-email-ldufour@linux.vnet.ibm.com> <2cb8256d-5822-d94d-b0e6-c46f21d84852@infradead.org> From: Laurent Dufour Date: Tue, 22 May 2018 13:47:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <2cb8256d-5822-d94d-b0e6-c46f21d84852@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18052211-0044-0000-0000-000005552541 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18052211-0045-0000-0000-00002896B22E Message-Id: <8a4016fb-2c2f-ad9a-9dd4-0ed3e664b659@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-05-22_03:,, 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=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805220138 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/05/2018 18:36, Randy Dunlap wrote: > Hi, > > On 05/17/2018 04:06 AM, Laurent Dufour wrote: >> This configuration variable will be used to build the code needed to >> handle speculative page fault. >> >> By default it is turned off, and activated depending on architecture >> support, ARCH_HAS_PTE_SPECIAL, SMP and MMU. >> >> The architecture support is needed since the speculative page fault handler >> is called from the architecture's page faulting code, and some code has to >> be added there to handle the speculative handler. >> >> The dependency on ARCH_HAS_PTE_SPECIAL is required because vm_normal_page() >> does processing that is not compatible with the speculative handling in the >> case ARCH_HAS_PTE_SPECIAL is not set. >> >> Suggested-by: Thomas Gleixner >> Suggested-by: David Rientjes >> Signed-off-by: Laurent Dufour >> --- >> mm/Kconfig | 22 ++++++++++++++++++++++ >> 1 file changed, 22 insertions(+) >> >> diff --git a/mm/Kconfig b/mm/Kconfig >> index 1d0888c5b97a..a38796276113 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -761,3 +761,25 @@ config GUP_BENCHMARK >> >> config ARCH_HAS_PTE_SPECIAL >> bool >> + >> +config ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT >> + def_bool n >> + >> +config SPECULATIVE_PAGE_FAULT >> + bool "Speculative page faults" >> + default y >> + depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT >> + depends on ARCH_HAS_PTE_SPECIAL && MMU && SMP >> + help >> + Try to handle user space page faults without holding the mmap_sem. >> + >> + This should allow better concurrency for massively threaded process > > processes > >> + since the page fault handler will not wait for other threads memory > > thread's > >> + layout change to be done, assuming that this change is done in another >> + part of the process's memory space. This type of page fault is named >> + speculative page fault. >> + >> + If the speculative page fault fails because of a concurrency is > > because a concurrency is > >> + detected or because underlying PMD or PTE tables are not yet >> + allocating, it is failing its processing and a classic page fault > > allocated, the speculative page fault fails and a classic page fault > >> + is then tried. > > > Also, all of the help text (below the "help" line) should be indented by > 1 tab + 2 spaces (in coding-style.rst). Thanks, Randy for reviewing my miserable English grammar. I'll fix that and the indentation.