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s=arc-20220608; d=hostedemail.com; t=1690597430; a=rsa-sha256; cv=none; b=otvFxwJOhhtLKzGpv40SCyMeLlNo6MZKLaWPFqhgxLb4njkL9E/tmeZaTx8sSq8g8HI0hV KeQNMTQTXH+GNWELwtAIUlXWgSBcJtXShRKhPzwpvwVIuWObwFqMlKORhVuvMftqRkJJVO CKEQRpdcsvdvnecZ0wOwwryPrz/9Hjw= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=none; spf=none (imf22.hostedemail.com: domain of shikemeng@huaweicloud.com has no SPF policy when checking 45.249.212.51) smtp.mailfrom=shikemeng@huaweicloud.com; dmarc=none Received: from mail02.huawei.com (unknown [172.30.67.143]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4RCSwq2xkgz4f3nVB for ; Sat, 29 Jul 2023 10:23:39 +0800 (CST) Received: from [10.174.178.129] (unknown [10.174.178.129]) by APP4 (Coremail) with SMTP id gCh0CgC3h64reMRkx2Q4PA--.18707S2; Sat, 29 Jul 2023 10:23:40 +0800 (CST) Subject: Re: [PATCH 1/8] mm/compaction: avoid missing last page block in section after skip offline sections To: David Hildenbrand , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, baolin.wang@linux.alibaba.com, mgorman@techsingularity.net, willy@infradead.org References: <20230728171037.2219226-1-shikemeng@huaweicloud.com> <20230728171037.2219226-2-shikemeng@huaweicloud.com> <8d3f4a1d-b624-3e2f-653c-032833646dea@redhat.com> From: Kemeng Shi Message-ID: Date: Sat, 29 Jul 2023 10:23:38 +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 > > Can we add a short comment which kind of PFN we return (first pfn of first offline section after an online section)? > Hi David, thanks for the review. Sure, I will add comment to skip_offline_sections_reverse. -- Best wishes Kemeng Shi >> @@ -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); >>       } >>         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); > > > So block_start_pfn() will now point at the first PFN of the offline section. > > Confusing stuff, but I get the idea and I think it makes sense to me :) >