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c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1690870146; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DYJu1yduU+1scqQYL3D/1+BD+wzVO9OvkxZUG6Sxx34=; b=eQUFo6fRDFiM1TB0pitspYvs5gtRmBEnjJX5L66aBqffr/J/obyDdQ35vRg7Lo0SWIlTUB HkVXc1y7rY6jvfwPo5GhpMaV+Pi4qaopIBdzwsjuxkHpHR40GnQrdc6svwOC8xkptv6f3T 0p+/S9/dGmU0rwVLM/8z6vg50U02S3k= Received: from mail02.huawei.com (unknown [172.30.67.169]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4RFPnP464Wz4f3m7v for ; Tue, 1 Aug 2023 14:08:57 +0800 (CST) Received: from [10.174.178.129] (unknown [10.174.178.129]) by APP3 (Coremail) with SMTP id _Ch0CgC31CJ4ochkDuPnOA--.37939S2; Tue, 01 Aug 2023 14:08:58 +0800 (CST) Subject: Re: [PATCH 1/8] mm/compaction: avoid missing last page block in section after skip offline sections To: Baolin Wang , 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> From: Kemeng Shi Message-ID: <6921ae7e-0c30-0934-168c-9480ca30108f@huaweicloud.com> Date: Tue, 1 Aug 2023 14:08:56 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; 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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); -- Best wishes Kemeng Shi