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(p200300d82f42b000db8b7655f60f812b.dip0.t-ipconnect.de. [2003:d8:2f42:b000:db8b:7655:f60f:812b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45e015bf73csm12934595e9.11.2025.09.11.05.31.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Sep 2025 05:31:54 -0700 (PDT) Message-ID: Date: Thu, 11 Sep 2025 14:31:52 +0200 Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [v5 04/15] mm/huge_memory: implement device-private THP splitting 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> <20250908000448.180088-5-balbirs@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: <20250908000448.180088-5-balbirs@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Eah1nJ_QzpI6mWKuwf7n7bY4kGHPmP2SL3om_hsi-D4_1757593916 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 08.09.25 02:04, Balbir Singh wrote: > Add support for splitting device-private THP folios, enabling fallback > to smaller page sizes when large page allocation or migration fails. > > Key changes: > - split_huge_pmd(): Handle device-private PMD entries during splitting > - Preserve RMAP_EXCLUSIVE semantics for anonymous exclusive folios > - Skip RMP_USE_SHARED_ZEROPAGE for device-private entries as they > don't support shared zero page semantics > > 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 > --- > mm/huge_memory.c | 129 +++++++++++++++++++++++++++++++++-------------- > 1 file changed, 91 insertions(+), 38 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 337d8e3dd837..b720870c04b2 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2880,16 +2880,19 @@ 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)); > Indentation. But I do wonder if we want a helper to do a more efficient is_pmd_migration_entry() || is_pmd_device_private_entry() If only I could come up with a good name ... any ideas? is_non_present_folio_entry() maybe? Well, there is device-exclusive .... but that would not be reachable on these paths yet, ever. > count_vm_event(THP_SPLIT_PMD); > > @@ -2937,18 +2940,43 @@ 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)) { I hate this whole function. But maybe in this case it's better to just have here if (is_pmd_migration_entry(old_pmd)) { } else if (is_pmd_device_private_entry(old_pmd)) { There is not much shared code and the helps reduce the indentation level. > + 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)); Indentation. > + 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); Single line please, this is unreadable. > + 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; > + > + 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); > + } > + } > + > soft_dirty = pmd_swp_soft_dirty(old_pmd); > uffd_wp = pmd_swp_uffd_wp(old_pmd); > } else { > @@ -3034,30 +3062,49 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > * Note that NUMA hinting access restrictions are not transferred to > * avoid any possibility of altering permissions across VMAs. > */ > - if (freeze || pmd_migration) { > + if (freeze || !present) { Here too, I wonder if we should just handle device-private completely separately for now. > for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) { > pte_t entry; > - swp_entry_t swp_entry; > - > - if (write) > - swp_entry = make_writable_migration_entry( > - page_to_pfn(page + i)); > - else if (anon_exclusive) > - swp_entry = make_readable_exclusive_migration_entry( > - page_to_pfn(page + i)); > - else > - swp_entry = make_readable_migration_entry( > - page_to_pfn(page + i)); > - if (young) > - swp_entry = make_migration_entry_young(swp_entry); > - if (dirty) > - swp_entry = make_migration_entry_dirty(swp_entry); > - entry = swp_entry_to_pte(swp_entry); > - if (soft_dirty) > - entry = pte_swp_mksoft_dirty(entry); > - if (uffd_wp) > - entry = pte_swp_mkuffd_wp(entry); > - > + if (freeze || is_migration_entry(swp_entry)) { > + if (write) > + swp_entry = make_writable_migration_entry( > + page_to_pfn(page + i)); > + else if (anon_exclusive) > + swp_entry = make_readable_exclusive_migration_entry( > + page_to_pfn(page + i)); > + else > + swp_entry = make_readable_migration_entry( > + page_to_pfn(page + i)); > + if (young) > + swp_entry = make_migration_entry_young(swp_entry); > + if (dirty) > + swp_entry = make_migration_entry_dirty(swp_entry); > + entry = swp_entry_to_pte(swp_entry); > + if (soft_dirty) > + entry = pte_swp_mksoft_dirty(entry); > + if (uffd_wp) > + entry = pte_swp_mkuffd_wp(entry); > + } else { > + /* > + * anon_exclusive was already propagated to the relevant > + * pages corresponding to the pte entries when freeze > + * is false. > + */ > + if (write) > + swp_entry = make_writable_device_private_entry( > + page_to_pfn(page + i)); > + else > + swp_entry = make_readable_device_private_entry( > + page_to_pfn(page + i)); > + /* > + * Young and dirty bits are not progated via swp_entry > + */ > + entry = swp_entry_to_pte(swp_entry); > + if (soft_dirty) > + entry = pte_swp_mksoft_dirty(entry); > + if (uffd_wp) > + entry = pte_swp_mkuffd_wp(entry); > + } > VM_WARN_ON(!pte_none(ptep_get(pte + i))); > set_pte_at(mm, addr, pte + i, entry); > } > @@ -3084,7 +3131,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > } > pte_unmap(pte); > > - if (!pmd_migration) > + if (!is_pmd_migration_entry(*pmd)) > folio_remove_rmap_pmd(folio, page, vma); > if (freeze) > put_page(page); > @@ -3096,8 +3143,10 @@ 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 change. -- Cheers David / dhildenb