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 A07BAC7EE2E for ; Mon, 12 Jun 2023 10:31:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233584AbjFLKb3 (ORCPT ); Mon, 12 Jun 2023 06:31:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39208 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231137AbjFLKbG (ORCPT ); Mon, 12 Jun 2023 06:31:06 -0400 Received: from out199-17.us.a.mail.aliyun.com (out199-17.us.a.mail.aliyun.com [47.90.199.17]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AD4CC422A for ; Mon, 12 Jun 2023 03:12:09 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R311e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046051;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VkxCZ1s_1686564619; Received: from 30.97.48.52(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0VkxCZ1s_1686564619) by smtp.aliyun-inc.com; Mon, 12 Jun 2023 18:10:20 +0800 Message-ID: <337d90f3-7c95-d5b8-de30-fb72e441a18b@linux.alibaba.com> Date: Mon, 12 Jun 2023 18:10:38 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.11.2 Subject: Re: [PATCH] mm: compaction: skip memory hole rapidly when isolating migratable pages To: David Hildenbrand , "Huang, Ying" Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <8cc668b77c8eb2fa78058b3d81386ebed9c5a9cd.1686294549.git.baolin.wang@linux.alibaba.com> <87sfax6v7c.fsf@yhuang6-desk2.ccr.corp.intel.com> <55e05ac0-041d-75eb-4707-e053dc3f2976@redhat.com> From: Baolin Wang In-Reply-To: <55e05ac0-041d-75eb-4707-e053dc3f2976@redhat.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 On 6/12/2023 5:54 PM, David Hildenbrand wrote: > On 12.06.23 11:36, Baolin Wang wrote: >> >> >> On 6/12/2023 2:39 PM, Huang, Ying wrote: >>> Baolin Wang writes: >>> >>>> 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 >>>> --- >>>>    include/linux/mmzone.h | 10 ++++++++++ >>>>    mm/compaction.c        | 23 ++++++++++++++++++++++- >>>>    2 files changed, 32 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >>>> index 5a7ada0413da..87e6c535d895 100644 >>>> --- a/include/linux/mmzone.h >>>> +++ b/include/linux/mmzone.h >>>> @@ -2000,6 +2000,16 @@ static inline unsigned long >>>> next_present_section_nr(unsigned long section_nr) >>>>        return -1; >>>>    } >>>> +static inline unsigned long next_online_section_nr(unsigned long >>>> section_nr) >>>> +{ >>>> +    while (++section_nr <= __highest_present_section_nr) { >>>> +        if (online_section_nr(section_nr)) >>>> +            return section_nr; >>>> +    } >>>> + >>>> +    return -1UL; >>>> +} >>>> + >>>>    /* >>>>     * These are _only_ used during initialisation, therefore they >>>>     * can use __initdata ...  They could have names to indicate >>>> diff --git a/mm/compaction.c b/mm/compaction.c >>>> index 3398ef3a55fe..3a55fdd20c49 100644 >>>> --- a/mm/compaction.c >>>> +++ b/mm/compaction.c >>>> @@ -229,6 +229,21 @@ static void reset_cached_positions(struct zone >>>> *zone) >>>>                    pageblock_start_pfn(zone_end_pfn(zone) - 1); >>>>    } >>>> +static unsigned long skip_hole_pageblock(unsigned long start_pfn) >>>> +{ >>>> +    unsigned long next_online_nr; >>>> +    unsigned long start_nr = pfn_to_section_nr(start_pfn); >>>> + >>>> +    if (online_section_nr(start_nr)) >>>> +        return -1UL; >>> >>> Define a macro for the maigic "-1UL"?  Which is used for multiple times >>> in the patch. >> >> I am struggling to find a readable macro for these '-1UL', since the >> '-1UL' in next_online_section_nr() indicates that it can not find an >> online section. However the '-1' in skip_hole_pageblock() indicates that >> it can not find an online pfn. > > Maybe something like > > #define SECTION_NR_INVALID -1UL Actually we already have a NR_MEM_SECTIONS macro, which means it is an invalid section if the section nr >= NR_MEM_SECTIONS. So using NR_MEM_SECTIONS seems more suitable? >> So after more thinking, I will change to return 'NR_MEM_SECTIONS' if can >> not find next online section in next_online_section_nr(). And in >> skip_hole_pageblock(), I will change to return 0 if can not find next >> online pfn. What do you think? > > Well, 0 "might be" (and most likely is) a valid section number, so you'd > simulate some kind-of a wraparound. I guess I'd prefer > SECTION_NR_INVALID instead. 0 means can not find next online pfn number, not a section number in skip_hole_pageblock().