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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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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> 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