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b=BpzuDtiLH5DjM5xwj+bJZDUJd9H++v0wIsLaURYcHdL0CoI1iS/7Nfukchbsxnv3E lIZ1PabU334X9eotP8NB1uz/fIbH6JT7sY/5vYsQPYY5W9rkznQ824Ix3tKT9Gl0ki TDDxyTGZoq64m/k6l16BONshHAip9pM1EjyY4rZ0= Date: Mon, 22 Sep 2025 19:35:33 -0700 From: Andrew Morton To: Wei Yang Cc: Zi Yan , "Vishal Moola (Oracle)" , vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, wangkefeng.wang@huawei.com, linux-mm@kvack.org, Oscar Salvador Subject: Re: [PATCH] mm/compaction: fix low_pfn advance on isolating hugetlb Message-Id: <20250922193533.dd6081d78e9e98f47fdf8d3d@linux-foundation.org> In-Reply-To: <20250913001034.wt3iw4nyrmldblhg@master> References: <20250910092240.3981-1-richard.weiyang@gmail.com> <20250911012521.4p7kmxv46kwz5fz5@master> <5F7DCC9D-4CA2-4BA2-9EA8-F04C3883E289@nvidia.com> <20250911032751.khtgvdhcqzyf3rgr@master> <3DE28F4B-ACB1-468F-89B9-D7750D24BE4E@nvidia.com> <20250912010721.zd67xbfdava2u26e@master> <20250913001034.wt3iw4nyrmldblhg@master> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; 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I'm inclined to just drop the patch and to ask that issue be reopened. Comments? Thanks. From: Wei Yang Subject: mm/compaction: fix low_pfn advance on isolating hugetlb Date: Wed, 10 Sep 2025 09:22:40 +0000 Commit 56ae0bb349b4 ("mm: compaction: convert to use a folio in isolate_migratepages_block()") converts api from page to folio. But the low_pfn advance for hugetlb page seems wrong when low_pfn doesn't point to head page. Originally, if page is a hugetlb tail page, compound_nr() return 1, which means low_pfn only advance one in next iteration. After the change, low_pfn would advance more than the hugetlb range, since folio_nr_pages() always return total number of the large page. This results in skipping some range to isolate and then to migrate. The worst case for alloc_contig is it does all the isolation and migration, but finally find some range is still not isolated. And then undo all the work and try a new range. Advance low_pfn to the end of hugetlb. Link: https://lkml.kernel.org/r/20250910092240.3981-1-richard.weiyang@gmail.com Fixes: 56ae0bb349b4 ("mm: compaction: convert to use a folio in isolate_migratepages_block()") Signed-off-by: Wei Yang Cc: "Vishal Moola (Oracle)" Cc: Kefeng Wang Cc: Oscar Salvador Cc: Brendan Jackman Cc: Johannes Weiner Cc: Michal Hocko Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Wei Yang Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/compaction.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/compaction.c~mm-compaction-fix-low_pfn-advance-on-isolating-hugetlb +++ a/mm/compaction.c @@ -989,7 +989,7 @@ isolate_migratepages_block(struct compac * Hugepage was successfully isolated and placed * on the cc->migratepages list. */ - low_pfn += folio_nr_pages(folio) - 1; + low_pfn += folio_nr_pages(folio) - folio_page_idx(folio, page) - 1; goto isolate_success_no_list; } _