From nobody Mon Feb 9 08:01:24 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 385EA1E9B3A for ; Mon, 10 Nov 2025 06:37:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762756661; cv=none; b=ZvOzXrPXbGTezurRiGXVekYi86hMfb1ku6KqmWfbFJkYfPtQFKm1iQsEJXzB/AUn6RdWQPV7BMLM9CSv383YyFITdvWqfcu5grqaq7j7B/j3bre6c+HmV9Wp7Rxg05BWWxs4kVX+GQaE8t5DRs2eOTBbb+nqr6eUEz2MX/9/jJ8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762756661; c=relaxed/simple; bh=nSFao4n0OQNnd+aLIPLOqixqcRBctN+f3eYopUJOxj4=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version:Content-Type; b=UTVk6uw8GAHdv7VrbRcUEtq2k+siW/mPfjzEPRjav0PqJLTjOseTJRiX9HM3GJ958gOVylfmO0ctvVDgepo0x5evcJZKwxfjcWdBLqKle3dOI4uGCSkppSa43ve8i2tg9a+T0ccIjolwBnZCxvKPQPR2pe7VBJQhRonqDqnXD10= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7032A497; Sun, 9 Nov 2025 22:37:30 -0800 (PST) Received: from ergosum.cambridge.arm.com (ergosum.cambridge.arm.com [10.1.196.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id F02B63F66E; Sun, 9 Nov 2025 22:37:35 -0800 (PST) From: Anshuman Khandual To: linux-mm@kvack.org Cc: vishal.moola@gmail.com, Anshuman Khandual , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Matthew Wilcox , linux-kernel@vger.kernel.org Subject: [PATCH] mm/ptdesc: Derive from the compound head in page_ptdesc() Date: Mon, 10 Nov 2025 06:37:25 +0000 Message-Id: <20251110063725.3118037-1-anshuman.khandual@arm.com> X-Mailer: git-send-email 2.30.2 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" struct ptdesc (including all relevant helpers) support multi order compound pages. But page_ptdesc() coverts given page into its own ptdesc rather than deriving from its compound head as would have been expected otherwise. Just change the macro to fetch the struct ptdesc from the compound head instead, so that the same struct ptdesc is reached from all tail pages. Cc: Andrew Morton Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Matthew Wilcox Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Anshuman Khandual --- This applies on v6.18-rc5 Found via code inspection. Apparently struct ptdesc could represent a page table page which is multi order looking into helpers as ptdesc_nr_pages(), __pagetable_ctor/dtor() and pagetable_free() etc. Am I missing something ? include/linux/mm_types.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 90e5790c318f..f7107bc55d1e 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -604,9 +604,9 @@ static_assert(sizeof(struct ptdesc) <=3D sizeof(struct = page)); const struct ptdesc *: (const struct folio *)(pt), \ struct ptdesc *: (struct folio *)(pt))) =20 -#define page_ptdesc(p) (_Generic((p), \ - const struct page *: (const struct ptdesc *)(p), \ - struct page *: (struct ptdesc *)(p))) +#define page_ptdesc(p) (_Generic((p), \ + const struct page *: (const struct ptdesc *)_compound_head(p), \ + struct page *: (struct ptdesc *)_compound_head(p))) =20 #ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING static inline void ptdesc_pmd_pts_init(struct ptdesc *ptdesc) --=20 2.30.2