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[87.161.172.195]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-458705c4cacsm26765925e9.24.2025.07.24.10.40.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Jul 2025 10:40:39 -0700 (PDT) Message-ID: Date: Thu, 24 Jul 2025 19:40:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/3] khugepaged: Optimize __collapse_huge_page_copy_succeeded() by PTE batching To: Lorenzo Stoakes , Dev Jain Cc: akpm@linux-foundation.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmgsLPQFCRvGjuMACgkQTd4Q 9wD/g1o0bxAAqYC7gTyGj5rZwvy1VesF6YoQncH0yI79lvXUYOX+Nngko4v4dTlOQvrd/vhb 02e9FtpA1CxgwdgIPFKIuXvdSyXAp0xXuIuRPQYbgNriQFkaBlHe9mSf8O09J3SCVa/5ezKM OLW/OONSV/Fr2VI1wxAYj3/Rb+U6rpzqIQ3Uh/5Rjmla6pTl7Z9/o1zKlVOX1SxVGSrlXhqt kwdbjdj/csSzoAbUF/duDuhyEl11/xStm/lBMzVuf3ZhV5SSgLAflLBo4l6mR5RolpPv5wad GpYS/hm7HsmEA0PBAPNb5DvZQ7vNaX23FlgylSXyv72UVsObHsu6pT4sfoxvJ5nJxvzGi69U s1uryvlAfS6E+D5ULrV35taTwSpcBAh0/RqRbV0mTc57vvAoXofBDcs3Z30IReFS34QSpjvl Hxbe7itHGuuhEVM1qmq2U72ezOQ7MzADbwCtn+yGeISQqeFn9QMAZVAkXsc9Wp0SW/WQKb76 FkSRalBZcc2vXM0VqhFVzTb6iNqYXqVKyuPKwhBunhTt6XnIfhpRgqveCPNIasSX05VQR6/a OBHZX3seTikp7A1z9iZIsdtJxB88dGkpeMj6qJ5RLzUsPUVPodEcz1B5aTEbYK6428H8MeLq NFPwmknOlDzQNC6RND8Ez7YEhzqvw7263MojcmmPcLelYbfOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaCwtJQUJG8aPFAAKCRBN3hD3AP+DWlDnD/4k2TW+HyOOOePVm23F5HOhNNd7nNv3 Vq2cLcW1DteHUdxMO0X+zqrKDHI5hgnE/E2QH9jyV8mB8l/ndElobciaJcbl1cM43vVzPIWn 01vW62oxUNtEvzLLxGLPTrnMxWdZgxr7ACCWKUnMGE2E8eca0cT2pnIJoQRz242xqe/nYxBB /BAK+dsxHIfcQzl88G83oaO7vb7s/cWMYRKOg+WIgp0MJ8DO2IU5JmUtyJB+V3YzzM4cMic3 bNn8nHjTWw/9+QQ5vg3TXHZ5XMu9mtfw2La3bHJ6AybL0DvEkdGxk6YHqJVEukciLMWDWqQQ RtbBhqcprgUxipNvdn9KwNpGciM+hNtM9kf9gt0fjv79l/FiSw6KbCPX9b636GzgNy0Ev2UV m00EtcpRXXMlEpbP4V947ufWVK2Mz7RFUfU4+ETDd1scMQDHzrXItryHLZWhopPI4Z+ps0rB CQHfSpl+wG4XbJJu1D8/Ww3FsO42TMFrNr2/cmqwuUZ0a0uxrpkNYrsGjkEu7a+9MheyTzcm vyU2knz5/stkTN2LKz5REqOe24oRnypjpAfaoxRYXs+F8wml519InWlwCra49IUSxD1hXPxO WBe5lqcozu9LpNDH/brVSzHCSb7vjNGvvSVESDuoiHK8gNlf0v+epy5WYd7CGAgODPvDShGN g3eXuA== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: HrxBPN4u2gNQ1_1pZXY_woAlcE58rioArbA_h8CMz4c_1753378841 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 0DF74140013 X-Rspamd-Server: rspam06 X-Stat-Signature: wcdadmzyj171h189mjemeyjixgx6q4yu X-HE-Tag: 1753378845-946154 X-HE-Meta: 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 Q9jwZYX8 4Z8HURqOQAtpanN2gs548aYkWBdrLyDEP2fQihbb8RNCsIxxqw8ggueYUcI4/yus2svMP7VxrFtaUTB0nZSIs/abVKIodESlfsbJmRt/HI6h3BMpkwizw4FdWoIT5/4JnnlfZTqAlJCgk52hrBqU0M1OyqTg9ohDijoRjAMiky6ystxthXserCMmeIL/Q5jGAL0021XYB1mwKdlAxjcqMnpzCKW3/UqyEB7S3yjUk8WDpNpjzBTZYHNws4kUSsCl3k+kYJvxaTtXy2SHKS4yJCpavISFRWNPpWf8tnzSo813Z69CQlPsoJjfEoCp15XXUwylilQLKmezat8nBhn2RSELbGTBiN7w4KcYrkAkdZ5qDpBL+6YD2WGCWC5N376UqHfRArd/1c2+lV+YyEpWdEujDHBZzK9/q/WI5w8CX4KgWbk7XD3dx3qgOVZS+MLw3nhML11dgFLfZffEFmcCReHoN4Ul/ewGgcTw4P0D5lm9wRJZXQUO6ML4X0r7eGa358HdSPeXfN7P19PXRNJk+GS4lPICNabge6cNUR1EUDEnPcfzzi9AwWUstOX37F/d0Kv5o X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 24.07.25 19:32, Lorenzo Stoakes wrote: > Message-ID: <32843cfb-a70b-4dfb-965c-4e1b0623a1b4@lucifer.local> > Reply-To: > In-Reply-To: <20250724052301.23844-3-dev.jain@arm.com> > > NIT: Please don't capitalise 'Optimize' here. > > I think Andrew fixed this for you actually in the repo though :P > > On Thu, Jul 24, 2025 at 10:53:00AM +0530, Dev Jain wrote: >> Use PTE batching to batch process PTEs mapping the same large folio. An >> improvement is expected due to batching refcount-mapcount manipulation on >> the folios, and for arm64 which supports contig mappings, the number of >> TLB flushes is also reduced. >> >> Acked-by: David Hildenbrand >> Reviewed-by: Baolin Wang >> Signed-off-by: Dev Jain >> --- >> mm/khugepaged.c | 25 ++++++++++++++++++------- >> 1 file changed, 18 insertions(+), 7 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index a55fb1dcd224..f23e943506bc 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -700,12 +700,15 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte, >> spinlock_t *ptl, >> struct list_head *compound_pagelist) >> { >> + unsigned long end = address + HPAGE_PMD_SIZE; >> struct folio *src, *tmp; >> - pte_t *_pte; >> pte_t pteval; >> + pte_t *_pte; >> + unsigned int nr_ptes; >> >> - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; >> - _pte++, address += PAGE_SIZE) { >> + for (_pte = pte; _pte < pte + HPAGE_PMD_NR; _pte += nr_ptes, >> + address += nr_ptes * PAGE_SIZE) { >> + nr_ptes = 1; >> pteval = ptep_get(_pte); >> if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { >> add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); >> @@ -722,18 +725,26 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte, >> struct page *src_page = pte_page(pteval); >> >> src = page_folio(src_page); >> - if (!folio_test_large(src)) >> + >> + if (folio_test_large(src)) { >> + unsigned int max_nr_ptes = (end - address) >> PAGE_SHIFT; >> + >> + nr_ptes = folio_pte_batch(src, _pte, pteval, max_nr_ptes); >> + } else { >> release_pte_folio(src); >> + } >> + >> /* >> * ptl mostly unnecessary, but preempt has to >> * be disabled to update the per-cpu stats >> * inside folio_remove_rmap_pte(). >> */ >> spin_lock(ptl); >> - ptep_clear(vma->vm_mm, address, _pte); >> - folio_remove_rmap_pte(src, src_page, vma); >> + clear_ptes(vma->vm_mm, address, _pte, nr_ptes); >> + folio_remove_rmap_ptes(src, src_page, nr_ptes, vma); >> spin_unlock(ptl); >> - free_folio_and_swap_cache(src); >> + free_swap_cache(src); >> + folio_put_refs(src, nr_ptes); > > Hm one thing here though is the free_folio_and_swap_cache() does: > > free_swap_cache(folio); > if (!is_huge_zero_folio(folio)) > folio_put(folio); > > Whereas here you unconditionally reduce the reference count. Might this > cause issues with the shrinker version of the huge zero folio? > > Should this be: > > if (!is_huge_zero_folio(src)) > folio_put_refs(src, nr_ptes); > > Or do we otherwise avoid issues with this? The huge zero folio is never PTE-mapped. -- Cheers, David / dhildenb