From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 536F437B012; Mon, 17 Aug 2026 17:57:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786989463; cv=none; b=QgKf1iKx0c4ThPV7Lh2DCjgJIVRw3IiWJYOxDyjBhHo1XFYibTYPty+PD73DwIcw+INpeoS3NQM7P+Snm2RG6+cS2Tqw0d5Lt3AwjK5CwKefpC1NGJ+zRDwmfQTt5Zwc01ilyxmrYKmAQVXr8G66Jw7dUchU8EG5jNAqd5OkakM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786989463; c=relaxed/simple; bh=HpnmfGDDSMoxbUJUM/NFcevNEY7pZNmPRsJqEVj4ofM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XNTiEqwFSQLl5gRyiwZ/79xlOSjEL7TNEWaQfWnZ2Kp7kK+Un0M/s+C40+uoy4dz4gcy6E7mEuSOw3WLHNwnPL0TIRvgDSgYN03UuNd6CW231RCHBA7O9BOXMY5eOf24ULyPoyGPoH6HJEUkcoXqe64xCN/kL1TA6e5xpoDueF8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ReK/IXSP; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ReK/IXSP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E51E31F000E9; Mon, 17 Aug 2026 17:57:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786989460; bh=i2yF4c1OLwY8lWTysKwC0MTw86KJas6HJqgjleBRs4w=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ReK/IXSPH/4YsYTJZkaBfAvgKjwrfynlRf/qwsQFkzdMLro7PTAjFl9rXfwinda3h OoQWPkCFVlEV6OoqID/oSBHI8ah3Fjca17apx3QCIYgKh2gsIKiaUlyN5dcXI/LUJF V1rN0ix1OEhOTAkppuFKARsF75Ifu5mRR+sNJHDfI7Y0ICb8TnOEcnuqx+MskgGzaH xwtxbBHv+KboL/M9Zy5sQ63uKgAFzHv9K1ffro05lDfVoWmBsMZxmEPqm3/3DV7qyL xevV7ckBzNltGWxcfh3NH3aWU+NR6wb8BKE3bE8qmuL2QupgF99sxiHYIsLQolH8P+ awDL+LI2VFGxg== Message-ID: <4e8e208c-3aa4-4060-b0a2-499bc76d19fa@kernel.org> Date: Mon, 17 Aug 2026 19:57:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 02/57] mm: add pte_none_or_zero() To: Kiryl Shutsemau , akpm@linux-foundation.org, ljs@kernel.org, nico.pache@linux.dev Cc: baolin.wang@linux.alibaba.com, baohua@kernel.org, dev.jain@arm.com, hughd@google.com, lance.yang@linux.dev, liam@infradead.org, mhocko@suse.com, rppt@kernel.org, ryan.roberts@arm.com, shuah@kernel.org, surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org, ziy@nvidia.com, usama.anjum@arm.com, agordeev@linux.ibm.com, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, kas@kernel.org, jannh@google.com, willy@infradead.org, pfalcato@suse.de, rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org References: <20260816224609.308019-1-kirill@shutemov.name> <20260816224609.308019-3-kirill@shutemov.name> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/17/26 00:45, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > A PTE that is none and one that maps the shared zeropage both stand for > a page of zeroes the mapping does not own. Code that cares only about > the contents can treat the two alike. > > Move khugepaged's local helper for that test to pgtable.h, below the > is_zero_pfn() it is built on. > > migrate_vma_insert_page() open-codes the same test on the slot it is > about to fill. Convert it. It still tells none from the zeropage, but > only to decide whether there is an old mapping to flush. > > No functional change intended. > > Assisted-by: Claude-Code:claude-opus-5 > Signed-off-by: Kiryl Shutsemau (Meta) > --- > include/linux/pgtable.h | 17 +++++++++++++++++ > mm/khugepaged.c | 7 ------- > mm/migrate_device.c | 9 ++------- > 3 files changed, 19 insertions(+), 14 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index 8c093c119e5a..bbee6d31f015 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -2064,6 +2064,23 @@ static inline struct page *_zero_page(unsigned long addr) > > #ifdef CONFIG_MMU > > +/** > + * pte_none_or_zero - Does this PTE map nothing, or the shared zeropage? > + * @pte: The page table entry to test. > + * > + * A PTE that is none and one that maps the shared zeropage both stand for a > + * page of zeroes the mapping does not own, so code that only cares about the > + * contents can treat them alike. > + * > + * Return: %true if @pte is none or maps the shared zeropage. > + */ > +static inline bool pte_none_or_zero(pte_t pte) > +{ > + if (pte_none(pte)) > + return true; > + return pte_present(pte) && is_zero_pfn(pte_pfn(pte)); > +} (casually skimming over some patches) That's just a horrible function. :) If there is no pte_zero() then there also shouldn't be a pte_none_or_zero(). And in the code-base we have "pte_t pte_zero = {0}" which actually makes sense, but is not what we care about here. Just have an additional helper like: pte_maps_zero_page() pte_is_zero_page() pte_maps_zero_folio() pte_is_zero_folio() pte_zero_page() pte_zero_folio() And let the callers still spell both cases out. if (pte_none(pte) || pte_is_zero_page(pte)) /* Do something amazing */ (we have both is_zero_page() and is_zero_folio() I assume "zero page" is cleaner as this thing might soon no longer be a folio) -- Cheers, David