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(p200300d82f42b000db8b7655f60f812b.dip0.t-ipconnect.de. [2003:d8:2f42:b000:db8b:7655:f60f:812b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45e01575fadsm25690325e9.6.2025.09.11.05.42.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Sep 2025 05:42:06 -0700 (PDT) Message-ID: Date: Thu, 11 Sep 2025 14:42:04 +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: [v5 07/15] mm/memory/fault: add THP fault handling for zone device private pages To: Balbir Singh , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: damon@lists.linux.dev, dri-devel@lists.freedesktop.org, 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: <20250908000448.180088-1-balbirs@nvidia.com> <20250908000448.180088-8-balbirs@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: <20250908000448.180088-8-balbirs@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 08.09.25 02:04, Balbir Singh wrote: > Implement CPU fault handling for zone device THP entries through > do_huge_pmd_device_private(), enabling transparent migration of > device-private large pages back to system memory on CPU access. > > When the CPU accesses a zone device THP entry, the fault handler > calls the device driver's migrate_to_ram() callback to migrate > the entire large page back to system memory. > > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Zi Yan > Cc: Joshua Hahn > Cc: Rakie Kim > Cc: Byungchul Park > Cc: Gregory Price > Cc: Ying Huang > Cc: Alistair Popple > Cc: Oscar Salvador > Cc: Lorenzo Stoakes > Cc: Baolin Wang > Cc: "Liam R. Howlett" > Cc: Nico Pache > Cc: Ryan Roberts > Cc: Dev Jain > Cc: Barry Song > Cc: Lyude Paul > Cc: Danilo Krummrich > Cc: David Airlie > Cc: Simona Vetter > Cc: Ralph Campbell > Cc: Mika Penttilä > Cc: Matthew Brost > Cc: Francois Dugast > > Signed-off-by: Balbir Singh > --- > include/linux/huge_mm.h | 7 +++++++ > mm/huge_memory.c | 36 ++++++++++++++++++++++++++++++++++++ > mm/memory.c | 6 ++++-- > 3 files changed, 47 insertions(+), 2 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 23f124493c47..2c6a0c3c862c 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -496,6 +496,8 @@ static inline bool folio_test_pmd_mappable(struct folio *folio) > > vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf); > > +vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf); > + > extern struct folio *huge_zero_folio; > extern unsigned long huge_zero_pfn; > > @@ -675,6 +677,11 @@ static inline vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf) > return 0; > } > > +static inline vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf) > +{ Is this a VM_WARN_ON_ONCE() or similar? (Maybe BUILD_BUG is possible?) > + return 0; > +} > + > static inline bool is_huge_zero_folio(const struct folio *folio) > { > return false; > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index b720870c04b2..d634b2157a56 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1287,6 +1287,42 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf) > > } > > +vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf) > +{ > + struct vm_area_struct *vma = vmf->vma; > + vm_fault_t ret = 0; > + spinlock_t *ptl; > + swp_entry_t swp_entry; > + struct page *page; > + > + if (vmf->flags & FAULT_FLAG_VMA_LOCK) { > + vma_end_read(vma); > + return VM_FAULT_RETRY; > + } > + > + ptl = pmd_lock(vma->vm_mm, vmf->pmd); > + if (unlikely(!pmd_same(*vmf->pmd, vmf->orig_pmd))) { > + spin_unlock(ptl); > + return 0; > + } > + > + swp_entry = pmd_to_swp_entry(vmf->orig_pmd); > + page = pfn_swap_entry_to_page(swp_entry); > + vmf->page = page; > + vmf->pte = NULL; > + if (trylock_page(vmf->page)) { > + get_page(page); > + spin_unlock(ptl); > + ret = page_pgmap(page)->ops->migrate_to_ram(vmf); > + unlock_page(vmf->page); > + put_page(page); > + } else { > + spin_unlock(ptl); > + } > + > + return ret; > +} > + > /* > * always: directly stall for all thp allocations > * defer: wake kswapd and fail if not immediately available > diff --git a/mm/memory.c b/mm/memory.c > index d9de6c056179..860665f4b692 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -6298,8 +6298,10 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma, > vmf.orig_pmd = pmdp_get_lockless(vmf.pmd); > > if (unlikely(is_swap_pmd(vmf.orig_pmd))) { > - VM_BUG_ON(thp_migration_supported() && > - !is_pmd_migration_entry(vmf.orig_pmd)); > + if (is_device_private_entry( > + pmd_to_swp_entry(vmf.orig_pmd))) Single line please. But didn't we have a pmd helper for that? > + return do_huge_pmd_device_private(&vmf); > + > if (is_pmd_migration_entry(vmf.orig_pmd)) > pmd_migration_entry_wait(mm, vmf.pmd); > return 0; -- Cheers David / dhildenb