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lF+nxt9YGtiKWsEJC3F7dEhV1pEBgntKl0aE8FVtyQXXPOxXtzUEBOGUsME3xSz/paIdO1CAk653zEMWd1wJBR7A73Hbjob8hdk+N1ySLZUr275O9h2FmSnb6A0SvE5x9CKtojcrvuVfpQbSBt89ycLoNaoep2dULkh5jYJtBy3BBQrUoOI7gwY/sENw0rV5z0zWCNvFUpAspcFM0UyNIhLTcNP6lkBnOrGZ6X8x5CZwu9wz9ZoNa6sXZz1NxMexmQ/TmsEMw/U3khtx/UYopgieRpaGu4Q3dJJsOKvLSM5SMA7FduMdS4ky45gQD1TMiVqWp9Y2urfLe6AkG4XTq8/LUHfSNIsWT9hE4gH75Ysf1ZJqtdeDWBlTyBouikjYeSwVuKc74+fqB2l0KWRPIXDvX9mLwREeBHYdmL2lpMu95pEEoUlsdBh+FlavNbqrt22XzBFD/vrMzmOZYxAxBtRZbtSdjUyuRsfALCqlEjd35XoQei8MkdFSw9g01ftgTD0nAIxIN7sNRs5WzGO5If3HZe6mCTy5vHWDKFXkURGIQiozcL/GwP3LE/xO8nxB3Q1FgZ3SyXOkC4x39/dgbgHJ3Sv/eW0MXMnx/2QkobmAFpKhUVS4zaTnYu+EFXST4X7N7YDqVBDFP18w= 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 21:25, 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 th= e >> low_pfn advance for hugetlb page seems wrong when low_pfn doesn't poin= t >> 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 isolat= e_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 = iterate > 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? > >> goto isolate_success_no_list; >> } >> >> -- = >> 2.34.1 > > -- = > Wei Yang > Help you, Help me Best Regards, Yan, Zi