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 D3FF4EB64D9 for ; Thu, 15 Jun 2023 07:23:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244038AbjFOHXt (ORCPT ); Thu, 15 Jun 2023 03:23:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44560 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242220AbjFOHXh (ORCPT ); Thu, 15 Jun 2023 03:23:37 -0400 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D6A2910E3 for ; Thu, 15 Jun 2023 00:23:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1686813813; x=1718349813; h=from:to:cc:subject:references:date:in-reply-to: message-id:mime-version; bh=AyVzFXfvvX5OIfE/LFA/Rh5crB3M1AKei6Um2jAbSA4=; b=UNRh21sZfL4MefE+CWAy0EEnRinIjNAHOBh2igHbko1nDec82EaKqhdW 9EK3XRp7IUWm6Irb0NbqeF/khGmVO69tQrCvE2Gq0WC8FN3T/dCTGOH8l C6prLaX4d4f9fRz1ugA85b3YMRn3F1cdjD3I8beIQcmCV3fPiGh1gL8ze frIAj0ogoyXNK2XUQtkAfVap9RvRXUVXxlhUFxGcqGHej7xL/tIiIXGyt 8whZgxUkYE3OgRmvBpEJPy3ujKgVmcI4WvpWzbL/AakApTBUP5yf9DyuE Quvoo65xqUv3AE7FuuFWaqEyPMYF6KAmcmpJxU4wuKbDGBD8mN7VGbVVQ A==; X-IronPort-AV: E=McAfee;i="6600,9927,10741"; a="445206070" X-IronPort-AV: E=Sophos;i="6.00,244,1681196400"; d="scan'208";a="445206070" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2023 00:23:33 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10741"; a="777554265" X-IronPort-AV: E=Sophos;i="6.00,244,1681196400"; d="scan'208";a="777554265" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2023 00:23:31 -0700 From: "Huang, Ying" To: Baolin Wang Cc: Mel Gorman , , , , , Subject: Re: [PATCH v2] mm: compaction: skip memory hole rapidly when isolating migratable pages References: <770f9f61472b24b6bc89adbd71a77d9cf62bb54f.1686646361.git.baolin.wang@linux.alibaba.com> <20230614095501.m4porztaibchrgwx@techsingularity.net> <87ilbpo1d9.fsf@yhuang6-desk2.ccr.corp.intel.com> <5f340d98-4ee0-35a9-58ed-943834d68042@linux.alibaba.com> Date: Thu, 15 Jun 2023 15:22:02 +0800 In-Reply-To: <5f340d98-4ee0-35a9-58ed-943834d68042@linux.alibaba.com> (Baolin Wang's message of "Thu, 15 Jun 2023 11:59:00 +0800") Message-ID: <87fs6tfaw5.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Baolin Wang writes: > On 6/15/2023 11:22 AM, Huang, Ying wrote: >> Hi, Mel, >> Mel Gorman writes: >> >>> On Tue, Jun 13, 2023 at 04:55:04PM +0800, Baolin Wang wrote: >>>> On some machines, the normal zone can have a large memory hole like >>>> below memory layout, and we can see the range from 0x100000000 to >>>> 0x1800000000 is a hole. So when isolating some migratable pages, the >>>> scanner can meet the hole and it will take more time to skip the large >>>> hole. From my measurement, I can see the isolation scanner will take >>>> 80us ~ 100us to skip the large hole [0x100000000 - 0x1800000000]. >>>> >>>> So adding a new helper to fast search next online memory section >>>> to skip the large hole can help to find next suitable pageblock >>>> efficiently. With this patch, I can see the large hole scanning only >>>> takes < 1us. >>>> >>>> [ 0.000000] Zone ranges: >>>> [ 0.000000] DMA [mem 0x0000000040000000-0x00000000ffffffff] >>>> [ 0.000000] DMA32 empty >>>> [ 0.000000] Normal [mem 0x0000000100000000-0x0000001fa7ffffff] >>>> [ 0.000000] Movable zone start for each node >>>> [ 0.000000] Early memory node ranges >>>> [ 0.000000] node 0: [mem 0x0000000040000000-0x0000000fffffffff] >>>> [ 0.000000] node 0: [mem 0x0000001800000000-0x0000001fa3c7ffff] >>>> [ 0.000000] node 0: [mem 0x0000001fa3c80000-0x0000001fa3ffffff] >>>> [ 0.000000] node 0: [mem 0x0000001fa4000000-0x0000001fa402ffff] >>>> [ 0.000000] node 0: [mem 0x0000001fa4030000-0x0000001fa40effff] >>>> [ 0.000000] node 0: [mem 0x0000001fa40f0000-0x0000001fa73cffff] >>>> [ 0.000000] node 0: [mem 0x0000001fa73d0000-0x0000001fa745ffff] >>>> [ 0.000000] node 0: [mem 0x0000001fa7460000-0x0000001fa746ffff] >>>> [ 0.000000] node 0: [mem 0x0000001fa7470000-0x0000001fa758ffff] >>>> [ 0.000000] node 0: [mem 0x0000001fa7590000-0x0000001fa7ffffff] >>>> >>>> Signed-off-by: Baolin Wang >>> >>> This may only be necessary for non-contiguous zones so a check for >>> zone_contiguous could be made but I suspect the saving, if any, would be >>> marginal. >>> >>> However, it's subtle that block_end_pfn can end up in an arbirary location >>> past the end of the zone or past cc->free_pfn. As the "continue" will update >>> cc->migrate_pfn, that might lead to errors in the future. It would be a >>> lot safer to pass in cc->free_pfn and do two things with the value. First, >>> there is no point scanning for a valid online section past cc->free_pfn so >>> terminating after cc->free_pfn may save some cycles. Second, cc->migrate_pfn >>> does not end up with an arbitrary value which is a more defensive approach >>> to any future programming errors. >> I have thought about this before. Originally, I had thought that we >> were safe because cc->free_pfn should be in a online section and >> block_end_pfn should reach cc->free_pfn before the end of zone. But >> after checking more code and thinking about it again, I found that the >> underlying sections may go offline under us during compaction. So that, >> cc->free_pfn may be in a offline section or after the end of zone. So, >> you are right, we need to consider the range of block_end_pfn. >> But, if we thought in this way (memory online/offline at any time), >> it >> appears that we need to check whether the underlying section was >> offlined. For example, is it safe to use "pfn_to_page()" in >> "isolate_migratepages_block()"? Is it possible for the underlying >> section to be offlined under us? > > It is possible. There is a previous discussion[1] about the race > between pfn_to_online_page() and memory offline. > > [1] > https://lore.kernel.org/lkml/87zgc6buoq.fsf@nvidia.com/T/#m642d91bcc726437e1848b295bc57ce249c7ca399 Thank you very much for sharing! That answers my questions directly! Best Regards, Huang, Ying