From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756766AbcH2IxP (ORCPT ); Mon, 29 Aug 2016 04:53:15 -0400 Received: from mga02.intel.com ([134.134.136.20]:40176 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750860AbcH2IxO (ORCPT ); Mon, 29 Aug 2016 04:53:14 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.28,595,1464678000"; d="scan'208";a="1048570314" Subject: Re: [PATCH] thp: reduce usage of huge zero page's atomic counter To: Anshuman Khandual , Linux Memory Management List References: <57C3F72C.6030405@linux.vnet.ibm.com> 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 From: Aaron Lu Message-ID: <3b8deaf7-2e7b-ff22-be72-31b1a7ebb3eb@intel.com> Date: Mon, 29 Aug 2016 16:53:09 +0800 MIME-Version: 1.0 In-Reply-To: <57C3F72C.6030405@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/29/2016 04:49 PM, Anshuman Khandual wrote: > 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 ? Sorry, forgot to attach its link. It's this one: https://git.kernel.org/cgit/linux/kernel/git/wfg/vm-scalability.git And the above mentioned usemem is: https://git.kernel.org/cgit/linux/kernel/git/wfg/vm-scalability.git/tree/usemem.c Regards, Aaron