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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Peter Xu , Alex Williamson , kvm@vger.kernel.org, =?utf-8?B?TG/Dr2M=?= Molinari , Shuah Khan , linux-kselftest@vger.kernel.org, dri-devel@lists.freedesktop.org, Madhavan Srinivasan , "Ritesh Harjani (IBM)" , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jason Gunthorpe Subject: Re: [PATCH v4 1/4] mm/rmap: duplicate a PMD mapping as one in folio_dup_file_rmap_pmd() Message-ID: References: <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-0-66f00b7a564c@virtuozzo.com> <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-1-66f00b7a564c@virtuozzo.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-1-66f00b7a564c@virtuozzo.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 265AA40008 X-Stat-Signature: t69ak6m6tm1iugm33srwt163aqfgioxi X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792656437-486122 X-HE-Meta: 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 HrugSbmc Jm+p6Un8wiWuyjIi2O/+82fxl4kcRXieCQSyk58osDUBGVBQLiOC1QTv138waNO2aMdcgmlqIjvj28PCW9eqjg/6EHipJacslmpL4PQlehqI0H83njjZY4Y7eJeCLGQxKAh/lc/eM/Ok6yvpt6F45FPdLBxsI1taTzqeLFxRYqhBslm8NWfTJtmaalhhcNobcFxX4E2wZ0tRX5DHWvIi6NXCz5Eu6QOGtMDu9YQbmDazH/EuLHdsbxjGOrsgZmhezXi8swqkAPpkT5J8b7t7f9n064VwpiXfsrs2Jptrn/iQAH6xVjrBp9vMXEqLZs/SPkxTM7TqfpT6zHLdW3OHIpzpVYqSLVlL/wTkOH57oC4nafoZNSx0OpLx78IJqYJTNhT3YsqC4mRe/tKfdPMFSLqYRRaMoy399Lwl9hOrNzc4ofCHbGew3gE8Yvw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Oct 21, 2026 at 10:36:00PM +0200, Konstantin Khorenko wrote: > folio_dup_file_rmap_pmd() passes PGTABLE_LEVEL_PTE to > __folio_dup_file_rmap() for HPAGE_PMD_NR pages, so it adds HPAGE_PMD_NR > PTE mappings to the folio instead of one PMD mapping. Each unmap of the > PMD removes one PMD mapping: > > - the folio's mapcount never returns to zero, and removing the folio > from the page cache reports "Bad page cache", or hits a VM_BUG_ON > with CONFIG_DEBUG_VM; > - the first unmap already counts as the last one and drops the > PMD-mapped statistics while the other mm still maps the folio; > - the second one drives the entire mapcount below zero and drops them > again. > > The helper has no caller yet, the next patch adds the first one. Pass > PGTABLE_LEVEL_PMD, as folio_try_dup_anon_rmap_pmd() does. > > Fixes: d8ef5e311d7b ("mm/rmap: convert page_dup_file_rmap() to folio_dup_file_rmap_[pte|ptes|pmd]()") Was this a mistake in d8ef5e311d7b, or actually intentional for whatever reason? If the latter this shouldn't be a fixes. > Signed-off-by: Konstantin Khorenko > --- > include/linux/rmap.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index 0b332770abeed..7562017416094 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -558,7 +558,7 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio, > struct page *page, struct vm_area_struct *dst_vma) > { > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - __folio_dup_file_rmap(folio, page, HPAGE_PMD_NR, dst_vma, PGTABLE_LEVEL_PTE); > + __folio_dup_file_rmap(folio, page, HPAGE_PMD_NR, dst_vma, PGTABLE_LEVEL_PMD); > #else > WARN_ON_ONCE(true); > #endif > > -- > 2.43.0 > -- Cheers, Lorenzo