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 DN0uXvbs 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10 Sep 2025, at 21:35, Zi Yan wrote: > On 10 Sep 2025, at 21:25, Wei Yang wrote: > >> On Wed, Sep 10, 2025 at 09:22:40AM +0000, Wei Yang wrote: >>> 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. >>> >>> Signed-off-by: Wei Yang >>> Fixes: 56ae0bb349b4 ("mm: compaction: convert to use a folio in isolate= _migratepages_block()") >>> Cc: Kefeng Wang >>> Cc: Oscar Salvador >> >> Forgot to cc stable. >> >> Cc: > > Is there any bug report to justify the backport? Since it is more likely > to be a performance issue instead of a correctness issue. > >> >>> --- >>> mm/compaction.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/mm/compaction.c b/mm/compaction.c >>> index bf021b31c7ec..1e8f8eca318c 100644 >>> --- a/mm/compaction.c >>> +++ b/mm/compaction.c >>> @@ -989,7 +989,7 @@ isolate_migratepages_block(struct compact_control *= cc, unsigned long low_pfn, >>> * Hugepage was successfully isolated and placed >>> * on the cc->migratepages list. >>> */ >>> - low_pfn +=3D folio_nr_pages(folio) - 1; >>> + low_pfn +=3D folio_nr_pages(folio) - folio_page_idx(folio, page) -= 1; >> >> One question is why we advance compound_nr() in original version. >> >> Yes, there are several places advancing compound_nr(), but it seems to i= terate >> on the same large page and do the same thing and advance 1 again. >> >> Not sure which part story I missed. > > isolate_migratepages_block() starts from the beginning of a pageblock. > How likely the code hit in the middle of a hugetlb? > In addition, there are two other =E2=80=9Clow_pfn +=3D (1UL << order) - 1= =E2=80=9D in the if (PageHuge(page)), why not change them too if you think page can point to the middle of a hugetlb? Best Regards, Yan, Zi