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b=fdd8SQJSLXHHGJM+CTe5q0eusqLo4/Yvj6Hy+N/Kdr4TpdX80s8pu9YqSQPtU1RAo F0uIHpulEmevf26g2P+5GP91AAQGtijOfX2d/nR0pLfTIFybtsfyCfdnV9vddJZ6GB cMn/SiRohtSr3ditXEnGa+7K0U5oaJWNnZxfGSRnYEHmTTLDzEasOu+ss9NXQnLLs1 9ke0TAlhkOQ1EeRyY1uWxLihthGWstqA5D+7kFOmW2MwY9m318XGHjKXBcLBRZFU3z +yF0IH376OzpLjOpO3042tb2yP9n9VWCcQo5XB+T8UNEaSQC8v6VqzbdHx50/oXw8a 6/jn9/5CMHqxg== Message-ID: Date: Fri, 13 Nov 2026 19:27:56 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/hmm: skip NUMA balancing on protnone faults To: Matthew Auld , linux-mm@kvack.org Cc: dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Matthew Brost , =?UTF-8?Q?Mika_Penttil=C3=A4?= , Leon Romanovsky , Jason Gunthorpe References: <20261112-numa-v1-1-ad9cbca8f49a@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <20261112-numa-v1-1-ad9cbca8f49a@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: cspqgsrrdsumxgd9ua7rkeer6ufy68q8 X-Rspamd-Queue-Id: E20DA2000A X-Rspam-User: X-HE-Tag: 1794594965-408726 X-HE-Meta: U2FsdGVkX18+A//V9xeahtotiCn+CqDuMGN5wLOKACrRThFYqy096rYHh2hpdiWA0pOC1VfUFVuFN6VK1+lbIaiKspTv9yz9ejexewWj4KP/SsUhM5Xg4RuLXRqOCt3MXM1EQZEEx2MqO/gsRgxqMxROi+Nxmpq/pXuc0PxkRGcL12awD+iXJmNFRnKqToRGri27UBpB7USN5qE21DS/p9hsnYBK3FzSmPEZv4KbnxdqKQQkol2uD4d19FhVun6VEbDhsbDV8dPJa5xp5IkLM4XQdcImWRYKQBLMnPxEjp5s8eTiqi+O7na1EHZTHXZWxJDZYlOZq1nCTzmGh1dJM+/5j1W0fzMLl5oeCsbvDtc/oLTBwckV0ZclDTpzpAncNdKbxYViuhin22Eeuyoq74tSs6t65mjNA419TDwxP85F3cWoav1D3aA36dfJBJH3W6fRgIaZZ0p+jXK2vb4cQU3ifgVB+7p+8utcLS47sGb8ga7VShThRj51BEBhjIj0JejB3FQTxj5STkwEOgTlRRKl+G0I5kwtvgKHC3NPgIUlDweQC3LjH/BtFDxSE2ELDZ6IExoswm+KNjE86VQpf4mb4n1A3sz0Rve9cB0y57k98Xx+nR0h+1bwg9W5qnFhBPMz8x8jMnpcvsUoCNnUJME6dQOaA/zPqqzIfIlcQu7PEPm9Jl1cb/by7jlYzwAZdCgOTQzCFm+dNLhud3ynMgv+i4+I8Uw2xoOQ9zgko6dx3LM6FQbXk6PYZPq8h1eHwQ63mFt2l4+1H6sWgTT1hDsAr0b+jmwUq5AfAM0OAmSHKV+OZF4rJymrool7MfISrimH47QZJsi/NvdGhv2ldWJ41cL4MdmLXvoo7ctwfapeRhuF8rXTc+lJ9qsfEXGe/Cxw6bMLUDCwxEVSwSdzDEljjOjt2sry5+RQxkdktCL7Cp7+Cqz+qRDP0pNY+5rsCv8VE/BhxJItsyfvn0h XX4f+Ig3 vr3gBj4fZe7xh0gI39a1elo7JWu0ZDIHq4kghQZTBiSsFOEDykoVekAmqGHQ963XgBgfv5aBY/bYlTDCX9jkF9iKx7jE8XSGx/nHCqXmw811LZPNgtUYTO5X7XQokzLPTP+BbJENYk9FLX9nDsr7/tpPE8c38JbRPP6KMbcmEMu2DLUy0wUfgYL+Yi5PUGZQTGbng2R3/BCVFD/DquGxtpTXqv+9GZZzRBQMyB7ZU3LONxMUc87dDNFlEgRVI1ojbfJm9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/13/26 17:25, Matthew Auld wrote: > When automatic NUMA balancing marks a PTE or PMD as protnone > (PAGE_NONE), hmm_pte_need_fault() requests a fault to restore access > permissions, including _PAGE_RW when write access is needed. > > Calling handle_mm_fault() from hmm_do_fault() currently triggers NUMA > balancing in do_numa_page() and do_huge_pmd_numa_page(). When > hmm_range_fault() runs from a device driver or kworker context (such as > a GPU SVM or userptr rebind worker), folios get migrated toward the CPU > node executing the remote fault. > > Also, each folio migration invokes try_to_migrate_one() -> > mmu_notifier_invalidate_range_start(), which invalidates the > caller's mmu_interval_notifier while holding mmap_lock. That causes > hmm_range_fault() to abort with -EBUSY after every 2 MiB PMD and exhaust > its retry timeout on large buffers, which has been observed with large > imported Xe userptr buffers. > > Add FAULT_FLAG_NO_NUMA and set it in hmm_do_fault() so protnone entries > restore PTE/PMD permissions in-place without performing NUMA balancing, > matching GUP's default !FOLL_HONOR_NUMA_FAULT behaviour. Ehm, that's not how it works. GUP will not trigger a "special" fault and will try not triggering a fault and not restore permissions. It will try continuing, leaving the protnone pte as it is. See gup_can_follow_protnone(). For read-only access that should always work. For write-access we always trigger an ordinary fault and do NUMA migration etc. So FAULT_FLAG_NO_NUMA is doing something completely different and I don't agree with it. -- Cheers, David