From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D597C6FA8E for ; Tue, 27 Sep 2022 11:23:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232056AbiI0LXO (ORCPT ); Tue, 27 Sep 2022 07:23:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45754 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232067AbiI0LWg (ORCPT ); Tue, 27 Sep 2022 07:22:36 -0400 Received: from out30-54.freemail.mail.aliyun.com (out30-54.freemail.mail.aliyun.com [115.124.30.54]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF0AD138F18 for ; Tue, 27 Sep 2022 04:21:15 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R911e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046049;MF=xhao@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0VQrxzwn_1664277669; Received: from 30.240.98.177(mailfrom:xhao@linux.alibaba.com fp:SMTPD_---0VQrxzwn_1664277669) by smtp.aliyun-inc.com; Tue, 27 Sep 2022 19:21:11 +0800 Message-ID: <393d6318-aa38-01ed-6ad8-f9eac89bf0fc@linux.alibaba.com> Date: Tue, 27 Sep 2022 19:21:08 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [RFC 0/6] migrate_pages(): batch TLB flushing To: Huang Ying , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Zi Yan , Yang Shi , Baolin Wang , Oscar Salvador , Matthew Wilcox , yangyicong@hisilicon.com, v-songbaohua@oppo.com, 21cnbao@gmail.com References: <20220921060616.73086-1-ying.huang@intel.com> From: haoxin In-Reply-To: <20220921060616.73086-1-ying.huang@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi,  Huang 在 2022/9/21 下午2:06, Huang Ying 写道: > From: "Huang, Ying" > > Now, migrate_pages() migrate pages one by one, like the fake code as > follows, > > for each page > unmap > flush TLB > copy > restore map > > If multiple pages are passed to migrate_pages(), there are > opportunities to batch the TLB flushing and copying. That is, we can > change the code to something as follows, > > for each page > unmap > for each page > flush TLB > for each page > copy > for each page > restore map > > The total number of TLB flushing IPI can be reduced considerably. And > we may use some hardware accelerator such as DSA to accelerate the > page copying. > > So in this patch, we refactor the migrate_pages() implementation and > implement the TLB flushing batching. Base on this, hardware > accelerated page copying can be implemented. > > If too many pages are passed to migrate_pages(), in the naive batched > implementation, we may unmap too many pages at the same time. The > possibility for a task to wait for the migrated pages to be mapped > again increases. So the latency may be hurt. To deal with this > issue, the max number of pages be unmapped in batch is restricted to > no more than HPAGE_PMD_NR. That is, the influence is at the same > level of THP migration. > > We use the following test to measure the performance impact of the > patchset, > > On a 2-socket Intel server, > > - Run pmbench memory accessing benchmark > > - Run `migratepages` to migrate pages of pmbench between node 0 and > node 1 back and forth. > As the pmbench can not run on arm64 machine, so i use lmbench instead. I test case like this: (i am not sure whether it is reasonable, but it seems worked) ./bw_mem -N10000 10000m rd & time migratepages pid node0 node1 o/patch w/patch real 0m0.035s real 0m0.024s user 0m0.000s user 0m0.000s sys 0m0.035s sys 0m0.024s the migratepages time is reduced above 32%. But there has a problem, i see the batch flush is called by migrate_pages_batch try_to_unmap_flush arch_tlbbatch_flush(&tlb_ubc->arch); // there batch flush really work. But in arm64, the arch_tlbbatch_flush are not supported, becasue it not support CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH yet. So, the tlb batch flush means no any flush is did, it is a empty func. Maybe this patch can help solve this problem. https://lore.kernel.org/linux-arm-kernel/20220921084302.43631-1-yangyicong@huawei.com/T/