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(p200300d82f1d01004f8ebb13c3c7f854.dip0.t-ipconnect.de. [2003:d8:2f1d:100:4f8e:bb13:c3c7:f854]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b6f0c6b99sm116739135e9.4.2025.08.29.04.57.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 29 Aug 2025 04:57:24 -0700 (PDT) Message-ID: Date: Fri, 29 Aug 2025 13:57:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 11/36] mm: limit folio/compound page sizes in problematic kernel configs To: Lorenzo Stoakes Cc: linux-kernel@vger.kernel.org, Zi Yan , "Mike Rapoport (Microsoft)" , Alexander Potapenko , Andrew Morton , Brendan Jackman , Christoph Lameter , Dennis Zhou , Dmitry Vyukov , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux.dev, io-uring@vger.kernel.org, Jason Gunthorpe , Jens Axboe , Johannes Weiner , John Hubbard , kasan-dev@googlegroups.com, kvm@vger.kernel.org, "Liam R. Howlett" , Linus Torvalds , linux-arm-kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-ide@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Marco Elver , Marek Szyprowski , Michal Hocko , Muchun Song , netdev@vger.kernel.org, Oscar Salvador , Peter Xu , Robin Murphy , Suren Baghdasaryan , Tejun Heo , virtualization@lists.linux.dev, Vlastimil Babka , wireguard@lists.zx2c4.com, x86@kernel.org References: <20250827220141.262669-1-david@redhat.com> <20250827220141.262669-12-david@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: trk6BhEjYD1arh4FSTdiqIJJgW11A-xjmjQG5H42Snc_1756468646 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 7B76DA0004 X-Stat-Signature: ipfzqzsifbhtaa9af8foqq5ecdx9cwkq X-Rspam-User: X-HE-Tag: 1756468666-105248 X-HE-Meta: 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 xUGkGlvz RAUwUg+3RqWqeVJH3vJsekrh7wvv/BzvgD4PxXyMpsTf3aXfxdkDc+fD6K9PxwUw9Mz8iR+jGDvJV3VvQVOb/s56s3kHkgvbBGf0j5LLW/+epZfLn5VRl4r3HlCbazCo2m1gu3dD4g+4Tve14UW7xSQvlRlYn/85/lz+PEUaxWH0vdV9w5um4VUyD5wTu187JkghdKun7NljvHntaXrfimRiCeRtT3VYvLGJ0z0zJ0NscNUgSDbVXK6xc31e1mrdbt+upq25t9jPUFVkHPi7B177kJa3uW3Qt8Q37ww0+EJJZMfc7HEIYNnirl+erkNanmPjBNeBny3A8Va86h9+iVSMtu7igjPGTNCz13sx+EJeewergQjm1qX1t6DIO0M9nxmxzrSaliJAjeL39rjpdAtrYG4Vxa5aYz8sFfApccCw4W+4T1qx6K6eJnx76MWng2Sy7ee3znsqp/pM7bUwiyx/ZpA== 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 28.08.25 17:10, Lorenzo Stoakes wrote: > On Thu, Aug 28, 2025 at 12:01:15AM +0200, David Hildenbrand wrote: >> Let's limit the maximum folio size in problematic kernel config where >> the memmap is allocated per memory section (SPARSEMEM without >> SPARSEMEM_VMEMMAP) to a single memory section. >> >> Currently, only a single architectures supports ARCH_HAS_GIGANTIC_PAGE >> but not SPARSEMEM_VMEMMAP: sh. >> >> Fortunately, the biggest hugetlb size sh supports is 64 MiB >> (HUGETLB_PAGE_SIZE_64MB) and the section size is at least 64 MiB >> (SECTION_SIZE_BITS == 26), so their use case is not degraded. >> >> As folios and memory sections are naturally aligned to their order-2 size >> in memory, consequently a single folio can no longer span multiple memory >> sections on these problematic kernel configs. >> >> nth_page() is no longer required when operating within a single compound >> page / folio. >> >> Reviewed-by: Zi Yan >> Acked-by: Mike Rapoport (Microsoft) >> Signed-off-by: David Hildenbrand > > Realy great comments, like this! > > I wonder if we could have this be part of the first patch where you fiddle > with MAX_FOLIO_ORDER etc. but not a big deal. I think it belongs into this patch where we actually impose the restrictions. [...] >> +/* >> + * Only pages within a single memory section are guaranteed to be >> + * contiguous. By limiting folios to a single memory section, all folio >> + * pages are guaranteed to be contiguous. >> + */ >> +#define MAX_FOLIO_ORDER PFN_SECTION_SHIFT > > Hmmm, was this implicit before somehow? I mean surely by the fact as you say > that physical contiguity would not otherwise be guaranteed :)) Well, my patches until this point made sure that any attempt to use a larger folio would fail in a way that we could spot now if there is any offender. That is why before this change, nth_page() was required within a folio. Hope that clarifies it, thanks! -- Cheers David / dhildenb