From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751919AbdHHEIx (ORCPT ); Tue, 8 Aug 2017 00:08:53 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:47920 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750736AbdHHEIw (ORCPT ); Tue, 8 Aug 2017 00:08:52 -0400 Subject: Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page To: "Huang, Ying" , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrea Arcangeli , "Kirill A. Shutemov" , Nadia Yvette Chambers , Michal Hocko , Jan Kara , Matthew Wilcox , Hugh Dickins , Minchan Kim , Shaohua Li References: <20170807072131.8343-1-ying.huang@intel.com> From: Mike Kravetz Message-ID: Date: Mon, 7 Aug 2017 21:07:27 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170807072131.8343-1-ying.huang@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/07/2017 12:21 AM, Huang, Ying wrote: > From: Huang Ying > > Huge page helps to reduce TLB miss rate, but it has higher cache > footprint, sometimes this may cause some issue. For example, when > clearing huge page on x86_64 platform, the cache footprint is 2M. But > on a Xeon E5 v3 2699 CPU, there are 18 cores, 36 threads, and only 45M > LLC (last level cache). That is, in average, there are 2.5M LLC for > each core and 1.25M LLC for each thread. If the cache pressure is > heavy when clearing the huge page, and we clear the huge page from the > begin to the end, it is possible that the begin of huge page is > evicted from the cache after we finishing clearing the end of the huge > page. And it is possible for the application to access the begin of > the huge page after clearing the huge page. > > To help the above situation, in this patch, when we clear a huge page, > the order to clear sub-pages is changed. In quite some situation, we > can get the address that the application will access after we clear > the huge page, for example, in a page fault handler. Instead of > clearing the huge page from begin to end, we will clear the sub-pages > farthest from the the sub-page to access firstly, and clear the > sub-page to access last. This will make the sub-page to access most > cache-hot and sub-pages around it more cache-hot too. If we cannot > know the address the application will access, the begin of the huge > page is assumed to be the the address the application will access. > > With this patch, the throughput increases ~28.3% in vm-scalability > anon-w-seq test case with 72 processes on a 2 socket Xeon E5 v3 2699 > system (36 cores, 72 threads). The test case creates 72 processes, > each process mmap a big anonymous memory area and writes to it from > the begin to the end. For each process, other processes could be seen > as other workload which generates heavy cache pressure. At the same > time, the cache miss rate reduced from ~33.4% to ~31.7%, the > IPC (instruction per cycle) increased from 0.56 to 0.74, and the time > spent in user space is reduced ~7.9% > > Thanks Andi Kleen to propose to use address to access to determine the > order of sub-pages to clear. > > The hugetlbfs access address could be improved, will do that in > another patch. hugetlb_fault masks off the actual faulting address with, address &= huge_page_mask(h); before calling hugetlb_no_page. But, we could pass down the actual (unmasked) address to take advantage of this optimization for hugetlb faults as well. hugetlb_fault is the only caller of hugetlb_no_page, so this should be pretty straight forward. Were you thinking of additional improvements? -- Mike Kravetz