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Violators will be prosecuted for from ; Mon, 29 Aug 2016 18:50:00 +1000 Received: from d23relay10.au.ibm.com (d23relay10.au.ibm.com [9.190.26.77]) by d23dlp03.au.ibm.com (Postfix) with ESMTP id 250AD3578052 for ; Mon, 29 Aug 2016 18:49:58 +1000 (EST) Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.234.96]) by d23relay10.au.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u7T8nweB983408 for ; Mon, 29 Aug 2016 18:49:58 +1000 Received: from d23av01.au.ibm.com (localhost [127.0.0.1]) by d23av01.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u7T8nvmX013114 for ; Mon, 29 Aug 2016 18:49:57 +1000 Date: Mon, 29 Aug 2016 14:19:48 +0530 From: Anshuman Khandual MIME-Version: 1.0 Subject: Re: [PATCH] thp: reduce usage of huge zero page's atomic counter References: In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Message-Id: <57C3F72C.6030405@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Aaron Lu , Linux Memory Management List Cc: "'Kirill A. Shutemov'" , Dave Hansen , Tim Chen , Huang Ying , Andrew Morton , Vlastimil Babka , Jerome Marchand , Andrea Arcangeli , Mel Gorman , Ebru Akagunduz , linux-kernel@vger.kernel.org On 08/29/2016 12:01 PM, Aaron Lu wrote: > The global zero page is used to satisfy an anonymous read fault. If > THP(Transparent HugePage) is enabled then the global huge zero page is used. > The global huge zero page uses an atomic counter for reference counting > and is allocated/freed dynamically according to its counter value. > > CPU time spent on that counter will greatly increase if there are > a lot of processes doing anonymous read faults. This patch proposes a > way to reduce the access to the global counter so that the CPU load > can be reduced accordingly. > > To do this, a new flag of the mm_struct is introduced: MMF_USED_HUGE_ZERO_PAGE. > With this flag, the process only need to touch the global counter in > two cases: > 1 The first time it uses the global huge zero page; > 2 The time when mm_user of its mm_struct reaches zero. > > Note that right now, the huge zero page is eligible to be freed as soon > as its last use goes away. With this patch, the page will not be > eligible to be freed until the exit of the last process from which it > was ever used. > > And with the use of mm_user, the kthread is not eligible to use huge > zero page either. Since no kthread is using huge zero page today, there > is no difference after applying this patch. But if that is not desired, > I can change it to when mm_count reaches zero. > > Case used for test on Haswell EP: > usemem -n 72 --readonly -j 0x200000 100G Is this benchmark publicly available ? Does not seem to be this one https://github.com/gnubert/usemem.git, Does it ? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756734AbcH2IuH (ORCPT ); Mon, 29 Aug 2016 04:50:07 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:51572 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756540AbcH2IuG (ORCPT ); Mon, 29 Aug 2016 04:50:06 -0400 X-IBM-Helo: d23dlp02.au.ibm.com X-IBM-MailFrom: khandual@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Mon, 29 Aug 2016 14:19:48 +0530 From: Anshuman Khandual User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Aaron Lu , Linux Memory Management List CC: "'Kirill A. Shutemov'" , Dave Hansen , Tim Chen , Huang Ying , Andrew Morton , Vlastimil Babka , Jerome Marchand , Andrea Arcangeli , Mel Gorman , Ebru Akagunduz , linux-kernel@vger.kernel.org Subject: Re: [PATCH] thp: reduce usage of huge zero page's atomic counter References: In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16082908-0004-0000-0000-0000018C8D3C X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16082908-0005-0000-0000-000008904A82 Message-Id: <57C3F72C.6030405@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-08-29_04:,, 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=8.0.1-1604210000 definitions=main-1608290092 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/29/2016 12:01 PM, Aaron Lu wrote: > The global zero page is used to satisfy an anonymous read fault. If > THP(Transparent HugePage) is enabled then the global huge zero page is used. > The global huge zero page uses an atomic counter for reference counting > and is allocated/freed dynamically according to its counter value. > > CPU time spent on that counter will greatly increase if there are > a lot of processes doing anonymous read faults. This patch proposes a > way to reduce the access to the global counter so that the CPU load > can be reduced accordingly. > > To do this, a new flag of the mm_struct is introduced: MMF_USED_HUGE_ZERO_PAGE. > With this flag, the process only need to touch the global counter in > two cases: > 1 The first time it uses the global huge zero page; > 2 The time when mm_user of its mm_struct reaches zero. > > Note that right now, the huge zero page is eligible to be freed as soon > as its last use goes away. With this patch, the page will not be > eligible to be freed until the exit of the last process from which it > was ever used. > > And with the use of mm_user, the kthread is not eligible to use huge > zero page either. Since no kthread is using huge zero page today, there > is no difference after applying this patch. But if that is not desired, > I can change it to when mm_count reaches zero. > > Case used for test on Haswell EP: > usemem -n 72 --readonly -j 0x200000 100G Is this benchmark publicly available ? Does not seem to be this one https://github.com/gnubert/usemem.git, Does it ?