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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b5753528csm153414105e9.3.2025.08.26.08.19.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Aug 2025 08:19:15 -0700 (PDT) Message-ID: <763e1fca-e4c4-467e-a1d0-ea911cad4714@redhat.com> Date: Tue, 26 Aug 2025 17:19:14 +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 From: David Hildenbrand 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> Content-Language: en-US In-Reply-To: <20250812024036.690064-3-balbirs@nvidia.com> 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 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12.08.25 04:40, Balbir Singh wrote: > Make THP handling code in the mm subsystem for THP pages aware of zone > device pages. Although the code is designed to be generic when it comes > to handling splitting of pages, the code is designed to work for THP > page sizes corresponding to HPAGE_PMD_NR. > > Modify page_vma_mapped_walk() to return true when a zone device huge > entry is present, enabling try_to_migrate() and other code migration > paths to appropriately process the entry. page_vma_mapped_walk() will > return true for zone device private large folios only when > PVMW_THP_DEVICE_PRIVATE is passed. This is to prevent locations that are > not zone device private pages from having to add awareness. Please don't if avoidable. We should already have the same problem with small zone-device private pages, and should have proper folio checks in place, no? [...] This thing is huge and hard to review. Given there are subtle changes in here that are likely problematic, this is a problem. Is there any way to split this into logical chunks? 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 ;) > > struct page_vma_mapped_walk { > unsigned long pfn; > diff --git a/include/linux/swapops.h b/include/linux/swapops.h > index 64ea151a7ae3..2641c01bd5d2 100644 > --- a/include/linux/swapops.h > +++ b/include/linux/swapops.h > @@ -563,6 +563,7 @@ static inline int is_pmd_migration_entry(pmd_t pmd) > { > return is_swap_pmd(pmd) && is_migration_entry(pmd_to_swp_entry(pmd)); > } > + ^ unrelated change > #else /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ > static inline int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, > struct page *page) > @@ -594,6 +595,22 @@ static inline int is_pmd_migration_entry(pmd_t pmd) > } > #endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ > > +#if defined(CONFIG_ZONE_DEVICE) && defined(CONFIG_ARCH_ENABLE_THP_MIGRATION) > + > +static inline int is_pmd_device_private_entry(pmd_t pmd) > +{ > + return is_swap_pmd(pmd) && is_device_private_entry(pmd_to_swp_entry(pmd)); > +} > + > +#else /* CONFIG_ZONE_DEVICE && CONFIG_ARCH_ENABLE_THP_MIGRATION */ > + > +static inline int is_pmd_device_private_entry(pmd_t pmd) > +{ > + return 0; > +} > + > +#endif /* CONFIG_ZONE_DEVICE && CONFIG_ARCH_ENABLE_THP_MIGRATION */ > + > static inline int non_swap_entry(swp_entry_t entry) > { > return swp_type(entry) >= MAX_SWAPFILES; > diff --git a/lib/test_hmm.c b/lib/test_hmm.c > index 761725bc713c..297f1e034045 100644 > --- a/lib/test_hmm.c > +++ b/lib/test_hmm.c > @@ -1408,7 +1408,7 @@ static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf) > * the mirror but here we use it to hold the page for the simulated > * device memory and that page holds the pointer to the mirror. > */ > - rpage = vmf->page->zone_device_data; > + rpage = folio_page(page_folio(vmf->page), 0)->zone_device_data; Can we have a wrapper please to give us the zone_device_data for a folio, so we have something like rpage = folio_zone_device_data(page_folio(vmf->page)); > dmirror = rpage->zone_device_data; > > /* FIXME demonstrate how we can adjust migrate range */ > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 9c38a95e9f09..2495e3fdbfae 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1711,8 +1711,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > if (unlikely(is_swap_pmd(pmd))) { > swp_entry_t entry = pmd_to_swp_entry(pmd); > > - VM_BUG_ON(!is_pmd_migration_entry(pmd)); > - if (!is_readable_migration_entry(entry)) { > + VM_WARN_ON(!is_pmd_migration_entry(pmd) && > + !is_pmd_device_private_entry(pmd)); > + > + if (is_migration_entry(entry) && > + is_writable_migration_entry(entry)) { > entry = make_readable_migration_entry( > swp_offset(entry)); 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. > pmd = swp_entry_to_pmd(entry); > @@ -1722,6 +1725,32 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > pmd = pmd_swp_mkuffd_wp(pmd); > set_pmd_at(src_mm, addr, src_pmd, pmd); > } > + > + if (is_device_private_entry(entry)) { likely you want "else if" here. > + if (is_writable_device_private_entry(entry)) { > + entry = make_readable_device_private_entry( > + swp_offset(entry)); > + pmd = swp_entry_to_pmd(entry); > + > + if (pmd_swp_soft_dirty(*src_pmd)) > + pmd = pmd_swp_mksoft_dirty(pmd); > + if (pmd_swp_uffd_wp(*src_pmd)) > + pmd = pmd_swp_mkuffd_wp(pmd); > + set_pmd_at(src_mm, addr, src_pmd, pmd); > + } > + > + src_folio = pfn_swap_entry_folio(entry); > + VM_WARN_ON(!folio_test_large(src_folio)); > + > + folio_get(src_folio); > + /* > + * folio_try_dup_anon_rmap_pmd does not fail for > + * device private entries. > + */ > + VM_WARN_ON(folio_try_dup_anon_rmap_pmd(src_folio, > + &src_folio->page, dst_vma, src_vma)); > + } I would appreciate if this code flow here would resemble more what we have in copy_nonpresent_pte(), at least regarding handling of these two cases. (e.g., dropping the VM_WARN_ON) > + > add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR); > mm_inc_nr_ptes(dst_mm); > pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable); > @@ -2219,15 +2248,22 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > folio_remove_rmap_pmd(folio, page, vma); > WARN_ON_ONCE(folio_mapcount(folio) < 0); > VM_BUG_ON_PAGE(!PageHead(page), page); > - } else if (thp_migration_supported()) { > + } else if (is_pmd_migration_entry(orig_pmd) || > + is_pmd_device_private_entry(orig_pmd)) { > swp_entry_t entry; > > - VM_BUG_ON(!is_pmd_migration_entry(orig_pmd)); > entry = pmd_to_swp_entry(orig_pmd); > folio = pfn_swap_entry_folio(entry); > flush_needed = 0; > - } else > - 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. > + } > + } > > if (folio_test_anon(folio)) { > zap_deposited_table(tlb->mm, pmd); > @@ -2247,6 +2283,15 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > folio_mark_accessed(folio); > } > > + /* > + * Do a folio put on zone device private pages after > + * changes to mm_counter, because the folio_put() will > + * clean folio->mapping and the folio_test_anon() check > + * will not be usable. > + */ The comment can be dropped: it's simple, don't use "folio" after dropping the reference when zapping. > + if (folio_is_device_private(folio)) > + folio_put(folio); > + > spin_unlock(ptl); > if (flush_needed) > tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE); > @@ -2375,7 +2420,8 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > struct folio *folio = pfn_swap_entry_folio(entry); > pmd_t newpmd; > > - VM_BUG_ON(!is_pmd_migration_entry(*pmd)); > + VM_WARN_ON(!is_pmd_migration_entry(*pmd) && > + !folio_is_device_private(folio)); > if (is_writable_migration_entry(entry)) { > /* > * A protection check is difficult so > @@ -2388,6 +2434,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > newpmd = swp_entry_to_pmd(entry); > if (pmd_swp_soft_dirty(*pmd)) > newpmd = pmd_swp_mksoft_dirty(newpmd); > + } else if (is_writable_device_private_entry(entry)) { > + entry = make_readable_device_private_entry( > + swp_offset(entry)); > + newpmd = swp_entry_to_pmd(entry); > } else { > newpmd = *pmd; > } > @@ -2842,16 +2892,19 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > struct page *page; > pgtable_t pgtable; > pmd_t old_pmd, _pmd; > - bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false; > - bool anon_exclusive = false, dirty = false; > + bool young, write, soft_dirty, uffd_wp = false; > + bool anon_exclusive = false, dirty = false, present = false; > unsigned long addr; > pte_t *pte; > int i; > + swp_entry_t swp_entry; > > VM_BUG_ON(haddr & ~HPAGE_PMD_MASK); > VM_BUG_ON_VMA(vma->vm_start > haddr, vma); > VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma); > - VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd)); > + > + VM_WARN_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd) > + && !(is_pmd_device_private_entry(*pmd))); VM_WARN_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd) && !(is_pmd_device_private_entry(*pmd))); > > count_vm_event(THP_SPLIT_PMD); > > @@ -2899,18 +2952,45 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > return __split_huge_zero_page_pmd(vma, haddr, pmd); > } > > - pmd_migration = is_pmd_migration_entry(*pmd); > - if (unlikely(pmd_migration)) { > - swp_entry_t entry; > > + present = pmd_present(*pmd); > + if (unlikely(!present)) { > + swp_entry = pmd_to_swp_entry(*pmd); > old_pmd = *pmd; > - entry = pmd_to_swp_entry(old_pmd); > - page = pfn_swap_entry_to_page(entry); > - write = is_writable_migration_entry(entry); > - if (PageAnon(page)) > - anon_exclusive = is_readable_exclusive_migration_entry(entry); > - young = is_migration_entry_young(entry); > - dirty = is_migration_entry_dirty(entry); > + > + folio = pfn_swap_entry_folio(swp_entry); > + VM_WARN_ON(!is_migration_entry(swp_entry) && > + !is_device_private_entry(swp_entry)); > + page = pfn_swap_entry_to_page(swp_entry); > + > + if (is_pmd_migration_entry(old_pmd)) { > + write = is_writable_migration_entry(swp_entry); > + if (PageAnon(page)) > + anon_exclusive = > + is_readable_exclusive_migration_entry( > + swp_entry); > + young = is_migration_entry_young(swp_entry); > + dirty = is_migration_entry_dirty(swp_entry); > + } else if (is_pmd_device_private_entry(old_pmd)) { > + write = is_writable_device_private_entry(swp_entry); > + anon_exclusive = PageAnonExclusive(page); > + if (freeze && anon_exclusive && > + folio_try_share_anon_rmap_pmd(folio, page)) > + freeze = false; > + if (!freeze) { > + rmap_t rmap_flags = RMAP_NONE; > + > + if (anon_exclusive) > + rmap_flags |= RMAP_EXCLUSIVE; > + > + folio_ref_add(folio, HPAGE_PMD_NR - 1); > + if (anon_exclusive) > + rmap_flags |= RMAP_EXCLUSIVE; > + folio_add_anon_rmap_ptes(folio, page, HPAGE_PMD_NR, > + vma, haddr, rmap_flags); > + } > + } This is massive and I'll have to review it with a fresh mind later. [...] put_page(page); > @@ -3058,8 +3157,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address, > pmd_t *pmd, bool freeze) > { > + ^ unrelated > VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE)); > - if (pmd_trans_huge(*pmd) || is_pmd_migration_entry(*pmd)) > + if (pmd_trans_huge(*pmd) || is_pmd_migration_entry(*pmd) || > + (is_pmd_device_private_entry(*pmd))) if (pmd_trans_huge(*pmd) || is_pmd_migration_entry(*pmd) || is_pmd_device_private_entry(*pmd)) > __split_huge_pmd_locked(vma, pmd, address, freeze); > } > > @@ -3238,6 +3339,9 @@ static void lru_add_split_folio(struct folio *folio, struct folio *new_folio, > VM_BUG_ON_FOLIO(folio_test_lru(new_folio), folio); > lockdep_assert_held(&lruvec->lru_lock); > > + if (folio_is_device_private(folio)) > + return; > + > if (list) { > /* page reclaim is reclaiming a huge page */ > VM_WARN_ON(folio_test_lru(folio)); > @@ -3252,6 +3356,7 @@ static void lru_add_split_folio(struct folio *folio, struct folio *new_folio, > list_add_tail(&new_folio->lru, &folio->lru); > folio_set_lru(new_folio); > } > + ^ unrelated > } > > /* Racy check whether the huge page can be split */ > @@ -3727,7 +3832,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > > /* Prevent deferred_split_scan() touching ->_refcount */ > spin_lock(&ds_queue->split_queue_lock); > - if (folio_ref_freeze(folio, 1 + extra_pins)) { > + if (folio_ref_freeze(folio, 1 + folio_expected_ref_count(folio))) { I think I discussed that with Zi Yan and it's tricky. Such a change should go into a separate cleanup patch. > struct address_space *swap_cache = NULL; > struct lruvec *lruvec; > int expected_refs; > @@ -3858,8 +3963,9 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > if (nr_shmem_dropped) > shmem_uncharge(mapping->host, nr_shmem_dropped); > > - if (!ret && is_anon) > + if (!ret && is_anon && !folio_is_device_private(folio)) > remap_flags = RMP_USE_SHARED_ZEROPAGE; > + ^ unrelated > remap_page(folio, 1 << order, remap_flags); > > /* > @@ -4603,7 +4709,10 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, > return 0; > > flush_cache_range(vma, address, address + HPAGE_PMD_SIZE); > - pmdval = pmdp_invalidate(vma, address, pvmw->pmd); > + if (unlikely(is_pmd_device_private_entry(*pvmw->pmd))) Use pmd_present() instead, please. (just like in the pte code that handles this). Why do we have to flush? pmd_clear() might be sufficient? In the PTE case we use pte_clear(). [...] > 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. > + pte_unmap_unlock(ptep, ptl); > + > + folio_get(folio); > + if (folio != fault_folio) > + folio_lock(folio); > + if (split_folio(folio)) { > + if (folio != fault_folio) > + folio_unlock(folio); > + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); > + goto next; > + } > + > + new_folio = page_folio(page); > + if (fault_folio) > + new_fault_folio = page_folio(migrate->fault_page); > + > + /* > + * Ensure the lock is held on the correct > + * folio after the split > + */ > + if (!new_fault_folio) { > + folio_unlock(folio); > + folio_put(folio); > + } else if (folio != new_fault_folio) { > + folio_get(new_fault_folio); > + folio_lock(new_fault_folio); > + folio_unlock(folio); > + folio_put(folio); > + } > + > + addr = start; > + goto again; Another thing to revisit with clean mind. > + } > + > mpfn = migrate_pfn(page_to_pfn(page)) | > MIGRATE_PFN_MIGRATE; > if (is_writable_device_private_entry(entry)) > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index e981a1a292d2..246e6c211f34 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -250,12 +250,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > pvmw->ptl = pmd_lock(mm, pvmw->pmd); > pmde = *pvmw->pmd; > if (!pmd_present(pmde)) { > - swp_entry_t entry; > + swp_entry_t entry = pmd_to_swp_entry(pmde); > > if (!thp_migration_supported() || > !(pvmw->flags & PVMW_MIGRATION)) > return not_found(pvmw); > - entry = pmd_to_swp_entry(pmde); > if (!is_migration_entry(entry) || > !check_pmd(swp_offset_pfn(entry), pvmw)) > return not_found(pvmw); > @@ -277,6 +276,16 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > * cannot return prematurely, while zap_huge_pmd() has > * cleared *pmd but not decremented compound_mapcount(). > */ > + swp_entry_t entry; > + > + entry = pmd_to_swp_entry(pmde); > + > + if (is_device_private_entry(entry) && > + (pvmw->flags & PVMW_THP_DEVICE_PRIVATE)) { > + pvmw->ptl = pmd_lock(mm, pvmw->pmd); > + return true; > + } > + > if ((pvmw->flags & PVMW_SYNC) && > thp_vma_suitable_order(vma, pvmw->address, > PMD_ORDER) && > diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c > index 567e2d084071..604e8206a2ec 100644 > --- a/mm/pgtable-generic.c > +++ b/mm/pgtable-generic.c > @@ -292,6 +292,12 @@ pte_t *___pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp) > *pmdvalp = pmdval; > if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval))) > goto nomap; > + if (is_swap_pmd(pmdval)) { > + swp_entry_t entry = pmd_to_swp_entry(pmdval); > + > + if (is_device_private_entry(entry)) > + goto nomap; > + } > if (unlikely(pmd_trans_huge(pmdval))) > goto nomap; > if (unlikely(pmd_bad(pmdval))) { > diff --git a/mm/rmap.c b/mm/rmap.c > index b5837075b6e0..f40e45564295 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2285,7 +2285,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > unsigned long address, void *arg) > { > struct mm_struct *mm = vma->vm_mm; > - DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); > + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, > + PVMW_THP_DEVICE_PRIVATE); > bool anon_exclusive, writable, ret = true; > pte_t pteval; > struct page *subpage; > @@ -2330,6 +2331,10 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > while (page_vma_mapped_walk(&pvmw)) { > /* PMD-mapped THP migration entry */ > if (!pvmw.pte) { > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > + unsigned long pfn; > +#endif > + > if (flags & TTU_SPLIT_HUGE_PMD) { > split_huge_pmd_locked(vma, pvmw.address, > pvmw.pmd, true); > @@ -2338,8 +2343,21 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > break; > } > #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > - subpage = folio_page(folio, > - pmd_pfn(*pvmw.pmd) - folio_pfn(folio)); > + /* > + * Zone device private folios do not work well with > + * pmd_pfn() on some architectures due to pte > + * inversion. > + */ Please use the handling for the PTE case as inspiration. /* * Handle PFN swap PTEs, such as device-exclusive ones, that * actually map pages. */ pteval = ptep_get(pvmw.pte); if (likely(pte_present(pteval))) { pfn = pte_pfn(pteval); } else { pfn = swp_offset_pfn(pte_to_swp_entry(pteval)); VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio); } So I would expect here something like /* * Handle PFN swap PTEs, such as device-exclusive ones, that * actually map pages. */ pmdval = pmdp_get(pvmw.pmd); if (likely(pmd_present(pmdval))) pfn = pmd_pfn(pmdval); else pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval)); > + if (is_pmd_device_private_entry(*pvmw.pmd)) { > + swp_entry_t entry = pmd_to_swp_entry(*pvmw.pmd); > + > + pfn = swp_offset_pfn(entry); > + } else { > + pfn = pmd_pfn(*pvmw.pmd); > + } > + > + subpage = folio_page(folio, pfn - folio_pfn(folio)); > + > VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) || > !folio_test_pmd_mappable(folio), folio); > -- Cheers David / dhildenb