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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7ebecb18cb4sm867878585a.2.2025.08.27.04.28.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Aug 2025 04:28:47 -0700 (PDT) Message-ID: <7cdc05d8-899b-495a-8298-ad5f27fcf8ad@redhat.com> Date: Wed, 27 Aug 2025 13:28:42 +0200 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: [v3 02/11] mm/thp: zone_device awareness in THP handling code To: Balbir Singh , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Andrew Morton , Zi Yan , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Oscar Salvador , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Ralph Campbell , =?UTF-8?Q?Mika_Penttil=C3=A4?= , Matthew Brost , Francois Dugast References: <20250812024036.690064-1-balbirs@nvidia.com> <20250812024036.690064-3-balbirs@nvidia.com> <763e1fca-e4c4-467e-a1d0-ea911cad4714@redhat.com> <85ef9a34-f511-4306-ac28-bf90f614709a@nvidia.com> From: David Hildenbrand Content-Language: en-US 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: <85ef9a34-f511-4306-ac28-bf90f614709a@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit >> Like teaching zap, mprotect, rmap walks .... code separately. >> >> I'm, sure you'll find a way to break this down so I don't walk out of a >> review with an headake ;) >> > > :) I had smaller chunks earlier, but then ran into don't add the change unless you > use the change problem > It's perfectly reasonable to have something like mm/huge_memory: teach copy_huge_pmd() about huge device-private entries mm/huge_memory: support splitting device-private folios ... etc :) [...] >> Careful: There is is_readable_exclusive_migration_entry(). So don't >> change the !is_readable_migration_entry(entry) to is_writable_migration_entry(entry)(), >> because it's wrong. >> > > Ack, I assume you are referring to potential prot_none entries? readable_exclusive are used to maintain the PageAnonExclusive bit right now for migration entries. So it's not realted to prot_none. [...] >>> -            WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!"); >>> + >>> +            if (!thp_migration_supported()) >>> +                WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!"); >>> + >>> +            if (is_pmd_device_private_entry(orig_pmd)) { >>> +                folio_remove_rmap_pmd(folio, &folio->page, vma); >>> +                WARN_ON_ONCE(folio_mapcount(folio) < 0); >> >> Can we jsut move that into the folio_is_device_private() check below. > > The check you mean? The whole thing like if (...) { folio_remove_rmap_pmd(folio, &folio->page, vma); WARN_ON_ONCE(folio_mapcount(folio) < 0); folio_put(folio) } [...] > >> Why do we have to flush? pmd_clear() might be sufficient? In the PTE case we use pte_clear(). > > Without the flush, other entities will not see the cleared pmd and isn't the pte_clear() only > when should_defer_flush() is true? It's a non-present page entry, so there should be no TLB entry to flush. > >> >> [...] >> >>>           pmde = pmd_mksoft_dirty(pmde); >>>       if (is_writable_migration_entry(entry)) >>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >>> index e05e14d6eacd..0ed337f94fcd 100644 >>> --- a/mm/migrate_device.c >>> +++ b/mm/migrate_device.c >>> @@ -136,6 +136,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, >>>                * page table entry. Other special swap entries are not >>>                * migratable, and we ignore regular swapped page. >>>                */ >>> +            struct folio *folio; >>> + >>>               entry = pte_to_swp_entry(pte); >>>               if (!is_device_private_entry(entry)) >>>                   goto next; >>> @@ -147,6 +149,51 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, >>>                   pgmap->owner != migrate->pgmap_owner) >>>                   goto next; >>>   +            folio = page_folio(page); >>> +            if (folio_test_large(folio)) { >>> +                struct folio *new_folio; >>> +                struct folio *new_fault_folio = NULL; >>> + >>> +                /* >>> +                 * The reason for finding pmd present with a >>> +                 * device private pte and a large folio for the >>> +                 * pte is partial unmaps. Split the folio now >>> +                 * for the migration to be handled correctly >>> +                 */ >> >> There are also other cases, like any VMA splits. Not sure if that makes a difference, >> the folio is PTE mapped. >> > > Ack, I can clarify that the folio is just pte mapped or remove the comment Sounds good. -- Cheers David / dhildenb