From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4B3863112DB; Mon, 12 Jan 2026 19:12:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768245120; cv=none; b=QBZIpRVh+OX7KkWJrEp3h2sNpKJjCU0yM/w6PSDrPvMSZt5Ahy0zX3KAfKC8TcfWQZZsQMIhtgKZQ6sjc63kDDvLeecy0zWZhmb4MoM7s2xnnx6Vwqps65xH99jJqd9MOHLr43Din3eJot6OcS+d/Sy36CfXYfyggTSw2g8Zn+M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768245120; c=relaxed/simple; bh=XcipN9fgKBFHcgoA+Nr6po6gwNQSSLcIPx8c1aOF+XQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IO5C76/nNeRKf1FSkVzMYFd0SBVHm2/QRrW4yoSaZrLB4iFJNjQeMv74IF40gYqtFGJUTJszN6IUfPoQV1eQBWZP73QSHsfczMdBzHEAshqklcBH4IdfHjaHV7pgKnilLz8uF8/iXjQ9OQ/Or3b1vHCzYlLyUe3yxC2N1+2/Zoc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=X7B4ifj1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="X7B4ifj1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E0584C116D0; Mon, 12 Jan 2026 19:11:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768245119; bh=XcipN9fgKBFHcgoA+Nr6po6gwNQSSLcIPx8c1aOF+XQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=X7B4ifj1p/c3HLp/4J2+Go8rjUoBtJGV50vA4sipb6J2chKy7E3TTr6yBwz6jIjNv y4MSvXhaziqYvaFOUgyptnQX32PjVB9WqHHzw9/7lrcV7Z8Sel+08VAsiJ/M4VBYy/ +QnWcc8DoF+EAqCa1miLOe3TDQNDd2SKy6GdpLmb097XMRJ72uD3mNOgqah76dtjwq Sv6B0s1LDNgEWBsU+ZdAxlXXozJ6aaQX1YtyKgKbSvYLcIUhKxTRXbE/tqjU1aOJsH 33mmqNurBRMC4Q73SgJyCnLQDkhQcQ6rgWEz57BZ4fQvIVplMKiWEyNwRR2nDJx039 m4i12kKYmQfIA== Message-ID: <746f5adb-1d91-4ca2-8ae0-a2d171203b66@kernel.org> Date: Mon, 12 Jan 2026 20:11:50 +0100 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: [PATCH v6 3/4] iommu: debug-pagealloc: Track IOMMU pages To: Mostafa Saleh , Jason Gunthorpe Cc: linux-mm@kvack.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, corbet@lwn.net, joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, xiaqinxin@huawei.com, baolu.lu@linux.intel.com, rdunlap@infradead.org, Samiullah Khawaja References: <20260109171805.901995-1-smostafa@google.com> <20260109171805.901995-4-smostafa@google.com> <20260109195111.GQ545276@ziepe.ca> <20260112133256.GB745888@ziepe.ca> <20260112135208.GD745888@ziepe.ca> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 1/12/26 15:58, Mostafa Saleh wrote: > On Mon, Jan 12, 2026 at 1:52 PM Jason Gunthorpe wrote: >> >> On Mon, Jan 12, 2026 at 01:43:41PM +0000, Mostafa Saleh wrote: >>> But I don’t see why not. from the documentation: >>> /** >>> * pfn_valid - check if there is a valid memory map entry for a PFN >>> * @pfn: the page frame number to check >>> * >>> * Check if there is a valid memory map entry aka struct page for the @pfn. >>> * Note, that availability of the memory map entry does not imply that >>> * there is actual usable memory at that @pfn. The struct page may >>> * represent a hole or an unusable page frame. >>> … >>> >>> That means that struct page exists, which is all what we need here. >> >> A struct page that has never been initialize shouldn't ever be read. I >> don't know how that relates to page_ext, but are you really sure that >> is all you need? >> > > AFAIU, if pfn_valid() returns true, it means the struct page is valid, > and lookup_page_ext() will check that a valid page_ext exists for this > entry. Not always. Offline memory blocks have a memory map but no page ext. We allocate the page ext at memory onlining time. Also, I'm not sure about ZONE_DEVICE memory, very likely we never allocate a page_ext for them? I'd assume both cases are not relevant for your use case, though. -- Cheers David