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 9E41AC41513 for ; Tue, 1 Aug 2023 08:00:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231825AbjHAIAy (ORCPT ); Tue, 1 Aug 2023 04:00:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231354AbjHAIAw (ORCPT ); Tue, 1 Aug 2023 04:00:52 -0400 Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com [115.124.30.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5B43D199F for ; Tue, 1 Aug 2023 01:00:50 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046060;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VooXfeW_1690876846; Received: from 30.97.48.66(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0VooXfeW_1690876846) by smtp.aliyun-inc.com; Tue, 01 Aug 2023 16:00:47 +0800 Message-ID: Date: Tue, 1 Aug 2023 16:01:14 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH 1/8] mm/compaction: avoid missing last page block in section after skip offline sections To: Kemeng Shi , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mgorman@techsingularity.net, willy@infradead.org, david@redhat.com References: <20230728171037.2219226-1-shikemeng@huaweicloud.com> <20230728171037.2219226-2-shikemeng@huaweicloud.com> <6e76323f-a1cc-7d20-676e-4eccdbcf6b91@linux.alibaba.com> <9b207dbf-1652-4851-7c6e-16220d5f2f3b@huaweicloud.com> <6921ae7e-0c30-0934-168c-9480ca30108f@huaweicloud.com> From: Baolin Wang In-Reply-To: <6921ae7e-0c30-0934-168c-9480ca30108f@huaweicloud.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 8/1/2023 2:08 PM, Kemeng Shi wrote: > > > on 8/1/2023 11:53 AM, Baolin Wang wrote: >> >> >> On 8/1/2023 10:36 AM, Kemeng Shi wrote: >>> >>> >>> on 8/1/2023 10:18 AM, Kemeng Shi wrote: >>>> >>>> >>>> on 7/31/2023 8:01 PM, Baolin Wang wrote: >>>>> >>>>> >>>>> On 7/29/2023 1:10 AM, Kemeng Shi wrote: >>>>>> skip_offline_sections_reverse will return the last pfn in found online >>>>>> section. Then we set block_start_pfn to start of page block which >>>>>> contains the last pfn in section. Then we continue, move one page >>>>>> block forward and ignore the last page block in the online section. >>>>>> Make block_start_pfn point to first page block after online section to fix >>>>>> this: >>>>>> 1. make skip_offline_sections_reverse return end pfn of online section, >>>>>> i.e. pfn of page block after online section. >>>>>> 2. assign block_start_pfn with next_pfn. >>>>>> >>>>>> Fixes: f63224525309 ("mm: compaction: skip the memory hole rapidly when isolating free pages") >>>>>> Signed-off-by: Kemeng Shi >>>>>> --- >>>>>>    mm/compaction.c | 5 ++--- >>>>>>    1 file changed, 2 insertions(+), 3 deletions(-) >>>>>> >>>>>> diff --git a/mm/compaction.c b/mm/compaction.c >>>>>> index 9b7a0a69e19f..ce7841363b12 100644 >>>>>> --- a/mm/compaction.c >>>>>> +++ b/mm/compaction.c >>>>>> @@ -259,7 +259,7 @@ static unsigned long skip_offline_sections_reverse(unsigned long start_pfn) >>>>>>          while (start_nr-- > 0) { >>>>>>            if (online_section_nr(start_nr)) >>>>>> -            return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION - 1; >>>>>> +            return section_nr_to_pfn(start_nr + 1); >>>>> >>>>> This is incorrect, you returned the start pfn of this section. >>>>> >>>>>>        } >>>>>>          return 0; >>>>>> @@ -1670,8 +1670,7 @@ static void isolate_freepages(struct compact_control *cc) >>>>>>                  next_pfn = skip_offline_sections_reverse(block_start_pfn); >>>>>>                if (next_pfn) >>>>>> -                block_start_pfn = max(pageblock_start_pfn(next_pfn), >>>>>> -                              low_pfn); >>>>>> +                block_start_pfn = max(next_pfn, low_pfn); >>>>> >>>>> 'block_start_pfn' should be pageblock aligned. If the 'next_pfn' is not pageblock-aligned (though this is not the common case), we should skip it. >>>>> >>>>> But if the 'next_pfn' is pageblock-aligned, yes, the commit f63224525309 still ignores the last pageblock, which is not right. So I think it should be: >>>>> block_start_pfn = pageblock_aligned(next_pfn) ? : pageblock_start_pfn(next_pfn); >>>>> block_start_pfn = max(block_start_pfn, low_pfn); >>>>> >>>> Hi Baolin, thanks for reply! As skip_offline_sections_reverse is based >>>> on skip_offline_sections. I make the assumption that section is pageblock >>>> aligned based on that we use section start from skip_offline_sections as >>>> block_start_fpn without align check. >>>> If section size is not pageblock aligned in real world, the pageblock aligned >>>> check should be added to skip_offline_sections and skip_offline_sections_reverse. >>>> If no one is against this, I will fix this in next version. THanks! >>>> >>> More information of aligment of section. For powerpc arch, we have SECTION_SIZE_BITS >>> with 24 while PAGE_SHIFT could be configured to 18. >>> Pageblock order is (18 + MAX_ORDER) which coule be 28 and is > SECTION_SZIE_BITS 24, >> >> The maximum pageblock order is MAX_ORDER. But after thinking more, I think return the start pfn or end pfn of a section is okay, and it should be aligned to a pageblock order IIUC. >> > Right, I mixed up the unit. >> So I think your change is good: >> + block_start_pfn = max(next_pfn, low_pfn); >> >> But in skip_offline_sections_reverse(), we should still return the last pfn of the online section. >> > Sure, then we should assign block_start_pfn with following change. Is this good to you? > - block_start_pfn = max(pageblock_start_pfn(next_pfn), > + block_start_pfn = max(pageblock_end_pfn(next_pfn), > low_pfn); The last pfn of a section is already section aligned, so I think no need to call pageblock_end_pfn(), just like your original change is okay to me. block_start_pfn = max(next_pfn, low_pfn);