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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Peter Xu , Alex Williamson , kvm@vger.kernel.org, =?utf-8?B?TG/Dr2M=?= Molinari , Lorenzo Stoakes , 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-Rspam-User: X-Rspamd-Queue-Id: 4F173C0009 X-Stat-Signature: e8ygjr9kntwaoiuxg3baxc55541khpc6 X-Rspamd-Server: rspam01 X-Spam-Status: No, score=-11.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793109199-315507 X-HE-Meta: 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 C90kIRqJ na306yaOTrjbuRgFkv1/QUECNj9cCuvWNq1355O86b6mUp+B16vs2LNvyI9KTSPWawwJ6l+/oRPM+IKhdES72c9tZlh094VbVBJWxxtEJlpp6U2QHqk+PyfkAnahu1lgMiLkGx+PTNScdWKcPUdRccljtij5mcxFznOmHfxApnSk7N6YaWkfof3X+3WkpHppro00+EMSixGeUnBMBe/e6hTd+T+/Xj24hE6d9lUhyngohrzdn+VQkcA4qORDOgs11zvl/Vtgb5G9feIW1ZLCL5ZEHRCsv+q84+SkWYcE8EMWZzSXs+0QYuEydREhbuaB3uPGoyy3Bzr+ALO4/F993BLpy+yW+N0Dkb8To0u8ovToWNZimaDqKyIFSPfovTiO5aYmGTNbQekgR6GDJCTWYHH9sxEEUZd7eoIAPEQFl2VmuNwmYYuqIwKtr4GG95yNUnLnZyYsjp1vpzWpb06g0dtBMdLujzvG50md7jGQnN3BTPvg= 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]()") > Signed-off-by: Konstantin Khorenko Reviewed-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov