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From devnull@lkml.org Wed May 1 02:14:54 2024 >From mailfetcher Wed Sep 28 05:33:39 2022 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on pi4 X-Spam-Level: X-Spam-Status: No, score=-0.9 required=5.0 tests=DMARC_NONE, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, RCVD_IN_ZEN_BLOCKED_OPENDNS,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.6 Authentication-Results: pi4.bmw12.nl; dmarc=none (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: pi4.bmw12.nl; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=2620:137:e000::1:20; helo=out1.vger.email; envelope-from=linux-kernel-owner@vger.kernel.org; receiver=) Received: from secure.jasper.es [188.166.10.231] by 1dc7d414a5be with IMAP (fetchmail-6.3.26) for (single-drop); Wed, 28 Sep 2022 05:33:39 +0200 (CEST) Received: from out1.vger.email (out1.vger.email [IPv6:2620:137:e000::1:20]) by pi4.bmw12.nl (Postfix) with ESMTP id 1429B3F055 for ; Wed, 28 Sep 2022 05:33:34 +0200 (CEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232463AbiI1DdZ (ORCPT ); Tue, 27 Sep 2022 23:33:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44900 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232378AbiI1DdV (ORCPT ); Tue, 27 Sep 2022 23 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 0B7718C008 for ; Tue, 27 Sep 2022 20:33:19 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R951e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045176;MF=xhao@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0VQuAZVs_1664335994; Received: from 30.240.98.9(mailfrom:xhao@linux.alibaba.com fp:SMTPD_---0VQuAZVs_1664335994) by smtp.aliyun-inc.com; Wed, 28 Sep 2022 11:33:16 +0800 Message-Id: <02e9da8a-39af-f6bd-b7f3-c60b3f2a59fb@linux.alibaba.com> Date: Wed, 28 Sep 2022 11:33:13 +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" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Zi Yan , Yang Shi , Baolin Wang , Oscar Salvador <393d6318-aa38-01ed-6ad8-f9eac89bf0fc@linux.alibaba.com> <874jws2r6o.fsf@yhuang6-desk2.ccr.corp.intel.com> From: haoxin In-Reply-To: <874jws2r6o.fsf@yhuang6-desk2.ccr.corp.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 在 2022/9/28 上午10:01, Huang, Ying 写道: > haoxin writes: > >> Hi, Huang >> >> ( 2022/9/21 H2:06, Huang Ying S: >>> 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. > Yes. And should_defer_flush() will always return false too. That is, > the TLB will still be flushed, but will not be batched. Oh, yes, i  ignore this, thank you. > >> Maybe this patch can help solve this problem. >> https://lore.kernel.org/linux-arm-kernel/20220921084302.43631-1-yangyicong@huawei.com/T/ > Yes. This will bring TLB flush batching to ARM64. Next time,  i will combine with this patch, and do some test again, do you have any suggestion about  benchmark ? > > Best Regards, > Huang, Ying