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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 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 X-Stat-Signature: h8d5o5nfeg53ytf5fxzjjfqwznz6fcyz X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 20AFCC0003 X-Rspam-User: X-HE-Tag: 1768245120-283621 X-HE-Meta: U2FsdGVkX1/QTS+rXgkGQ4g3Jum98uXyCwdnXF6nbDELX/I2+p0CG7naUX2NOTlNl8sW6EVLmWOBOetzILC/7PC3K34ck2nVOx6vwJqZut+NSnl4K5JR4Gu2HtS9BVY6UBHFfapVZ1vOvBvnrwfVf3+GzsHhQWQDYyP4zpEkGM/ADnTWeNxMU/GBujw9YTgQGrp5qJM3XauO0LiGWHTSfE6SB8iqlEjv6K/aMD6CLuXI9/Z1ErnRp9bu+EycvGS47Hx7bgLAzzyfflwGXdAkLZBr+13cU1pgskyHW+gDLHfM7gxLLaQvJby1P0U/dL03rOu4voeGbRMJqtQC7AmIwdnPU/2dck2SQX26wipXqi1E1fd116fMVF6R8ILyaNLQmLY5cwuJpunqsnfud43OMBojA1abSNnTkWL5CO5sYolY5uDisYzXtiGHa+g2K5E3eSN4mxP50eVPXSH18+aJSTQZqZylNCp1KzVbJgSZ3RABAoEV5qy6+pWOPWhopPhuAGeowGeMgpMUuwNflLfYLiLEriS89xFQIb1fAaQCNpsea0ZgGKKV1B5lNLxxgNAGAAVGixS/1C3qA4/d4t9OJgfqg4RRaKFc02qFQPT7ryP2WY/2JjDGB5KHof4VBIN93zWNr/a2yGYc3U5D2IPJirgYbggCvlEJfptjEUAYkjQ1rFG2NCsXTX9I7cznEI77+6njSWczm5JIceV3MjHzSFxS5qoe+Q/HX0k52Y195iBgKqeh08/XwJvLTyA2t2dMv94fyl8UuH0FB4rY51O7/JuLnmMNclaHWVRqIfOjv1xZXH6BP3Lf6MKj9ERQ92rLuq7yofBlDbwd7rMsLRcVfAifIl+51J/5lUx9Rrqf7WfuFJ5KFUyHKgMA3uocu3aNEVU3MiysrhoCzp3lel+QhVp1WWvi6RSaRZ9Ali+54iSgAoVh6aQLug5O3SKJ5yxlUFpYjL7Yi+SsxOdcmIJ On0SVFM2 7T/4TWpqbR2KUA3UJKkPyTZIT1pjZDGFoVkQQTfdVXvU9kbVPiwCxdFCpFRWF681od6TLURRL+2EV+5QtcJblh0Vg1VClGq6MFF6gaUNgTxSEfRjaY4Ba2d8FZz2xWtwC5yUCtykTuMg2rxDidlnBjDFoC4OtiHUpDMnJiJHBoTOMd+8HZ8NWKs5uHNnoUliNvDf/0wUsiuU0sQR7KvDB6Vs7f+bWCp8X/+jk0KylhggCeglDqLfTTdWRLABEpAqeErxMIwdPt2G6PWY3VUqTF4u8aB6jfSxWKlfFNkMjc7fjyoZqHDmIntVMTgBCJExsvjtb8ZjeCcz7I0Y9H7LJc+vAjA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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