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[148.163.156.1]) by mx.google.com with ESMTPS id z64si1862650ede.365.2019.04.23.08.22.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Apr 2019 08:22:04 -0700 (PDT) Received-SPF: pass (google.com: domain of ldufour@linux.ibm.com designates 148.163.156.1 as permitted sender) client-ip=148.163.156.1; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ldufour@linux.ibm.com designates 148.163.156.1 as permitted sender) smtp.mailfrom=ldufour@linux.ibm.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=ibm.com Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x3NFIuhR063362 for ; Tue, 23 Apr 2019 11:22:02 -0400 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0a-001b2d01.pphosted.com with ESMTP id 2s23rm4x93-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 23 Apr 2019 11:22:02 -0400 Received: from localhost by e06smtp03.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 23 Apr 2019 16:21:42 +0100 Received: from d06av24.portsmouth.uk.ibm.com (mk.ibm.com [9.149.105.60]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x3NFLfkJ26017998 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 23 Apr 2019 15:21:41 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DC7BC42045; Tue, 23 Apr 2019 15:21:40 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 678A04204D; Tue, 23 Apr 2019 15:21:38 +0000 (GMT) Received: from [9.145.7.116] (unknown [9.145.7.116]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 23 Apr 2019 15:21:38 +0000 (GMT) Subject: Re: [PATCH v12 01/31] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT To: Jerome Glisse Cc: 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 , aneesh.kumar@linux.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 , Ganesh Mahendran , Minchan Kim , Punit Agrawal , vinayak menon , Yang Shi , zhong jiang , Haiyan Song , Balbir Singh , sj38.park@gmail.com, Michel Lespinasse , Mike Rapoport , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, npiggin@gmail.com, paulmck@linux.vnet.ibm.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org References: <20190416134522.17540-1-ldufour@linux.ibm.com> <20190416134522.17540-2-ldufour@linux.ibm.com> <20190418214721.GA11645@redhat.com> From: Laurent Dufour Date: Tue, 23 Apr 2019 17:21:37 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190418214721.GA11645@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 19042315-0012-0000-0000-00000311DE1E X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19042315-0013-0000-0000-0000214A2FD2 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-23_04:,, 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 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904230103 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Le 18/04/2019 à 23:47, Jerome Glisse a écrit : > On Tue, Apr 16, 2019 at 03:44:52PM +0200, 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 > > Reviewed-by: Jérôme Glisse Thanks Jérôme. > Small question below > >> --- >> mm/Kconfig | 22 ++++++++++++++++++++++ >> 1 file changed, 22 insertions(+) >> >> diff --git a/mm/Kconfig b/mm/Kconfig >> index 0eada3f818fa..ff278ac9978a 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -761,4 +761,26 @@ 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 processes > > Is there any case where it does not provide better concurrency ? The > should make me wonder :) Depending on the VMA's type, it may not provide better concurrency. Indeed only anonymous mapping are managed currently. Perhaps this should be mentioned here, is it ? >> + since the page fault handler will not wait for other thread's memory >> + 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 a concurrent modification >> + is detected or because underlying PMD or PTE tables are not yet >> + allocated, the speculative page fault fails and a classic page fault >> + is then tried. >> + >> endmenu >> -- >> 2.21.0 >> >