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To: Zi Yan , Gregory Price Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org References: <20251020170615.1000819-1-gourry@gourry.net> <487730c6-423a-4a03-a668-9b9ff92a5cfb@redhat.com> <609E7E01-33A6-4931-AC89-1F4B2944FB64@nvidia.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: <609E7E01-33A6-4931-AC89-1F4B2944FB64@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: _S3oMKN06FsrilSoqZnPQO2S-IaZq4welogssF3hmPY_1760987919 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: jjph3dgbfinw3qm9bfa63g5myqg18ujn X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 27422180009 X-HE-Tag: 1760987923-451688 X-HE-Meta: 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 O0gWhVNU scTjfM4qOqD0PuHp0vsdXk6MNT0yt7TNWzGqDgsilYtkmgLc8Ru9QDZP3uV347azVv6Nx7ADGOf3sfofPHubal1FNdFoPYAs1M7VM9tJNQzFE+Rlo04jowkmjXUgj31z6SDZ3IZcRzH0Sf7Ywt8oLSaObXvl83HWY9tHT8sZFb2ogQbBHIvKFQK/+CHYehiyc32WOePm9UatFnRf51UcoJMCL3IUemo0Bo6CCIYw1LOsKu1Zs8a8Y0jyGZ5Ojo6kSqjMeJTH74Gcr57DlDNfWBIFcoKvhBlaUvN+2nOiqzwPEiNvwuU8OmyY9m2STaSShM+eX/4DrQs2J0qv+NAPYYpNqWWu1Kx6sFktJ9YKSPlloySMpZVHY0aMuCVzyqUVJekp2fgCR340CVEDHULO96I9jWPpzSXHCH9M6ZiQnoqcWnlzyJikR0XKCZQ== 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 20.10.25 21:15, Zi Yan wrote: > On 20 Oct 2025, at 13:41, Gregory Price wrote: > >> On Mon, Oct 20, 2025 at 07:24:04PM +0200, David Hildenbrand wrote: >>> On 20.10.25 19:06, Gregory Price wrote: >>> >>> Do we really need the folio_hugetlb_migratable() check? >>> This code is completely racy. >> >> My thought was it's better to check if any *one* folio in the bunch is >> non-migratable, it's better to never even call compaction in the first >> place. But you're right, this is racy. >> >> In one race, the compaction code will just fail if this bit gets set >> between now and the isolate call in folio_isolate_hugetlb() - resulting >> in searching the next block anyway. So that seemed ok? >> >> In the other race, the bit becomes un-set and we skip a block that might >> otherwise be valid. >> >> I can drop this check, it's just an optimistic optimization anyway. >> >> I should also probably check CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION here >> regardless, since we should skip compaction if migration isn't possible. >> >>>> folio_nr_pages() should be fine AFAIKT (no >>> VM_WARN_ON() etc), not sure about folio_test_hugetlb_migratable(). >> >> will change, and will check/change based on above thoughts. > > If it is racy, could folio_order() or folio_nr_pages() return a bogusly > large and cause a wrong result? > > In isolate_migratepages_block(), compound_order(page) is used and checked > against MAX_PAGE_ORDER to avoid a bogus page order. I wonder if we should > use the same pattern here. > > Basically, what is the right way of checking a folio order without lock? > Should we have a standardized helper function for that? As raised, snapshot_page() tries to stabilize the folio best it can. -- Cheers David / dhildenb