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(p200300cbc743de007030120fd1c94c3c.dip0.t-ipconnect.de. [2003:cb:c743:de00:7030:120f:d1c9:4c3c]) by smtp.gmail.com with ESMTPSA id wv11-20020a170907080b00b00a4503a78dd5sm9472229ejb.17.2024.04.04.11.52.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Apr 2024 11:52:19 -0700 (PDT) Message-ID: Date: Thu, 4 Apr 2024 20:52:16 +0200 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/7] mm: Add a bitmap into mmu_notifier_{clear,test}_young To: James Houghton , Andrew Morton , Paolo Bonzini Cc: Yu Zhao , David Matlack , Marc Zyngier , Oliver Upton , Sean Christopherson , Jonathan Corbet , James Morse , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Shaoqin Huang , Gavin Shan , Ricardo Koller , Raghavendra Rao Ananta , Ryan Roberts , David Rientjes , Axel Rasmussen , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org References: <20240401232946.1837665-1-jthoughton@google.com> <20240401232946.1837665-2-jthoughton@google.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20240401232946.1837665-2-jthoughton@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 02.04.24 01:29, James Houghton wrote: > The bitmap is provided for secondary MMUs to use if they support it. For > test_young(), after it returns, the bitmap represents the pages that > were young in the interval [start, end). For clear_young, it represents > the pages that we wish the secondary MMU to clear the accessed/young bit > for. > > If a bitmap is not provided, the mmu_notifier_{test,clear}_young() API > should be unchanged except that if young PTEs are found and the > architecture supports passing in a bitmap, instead of returning 1, > MMU_NOTIFIER_YOUNG_FAST is returned. > > This allows MGLRU's look-around logic to work faster, resulting in a 4% > improvement in real workloads[1]. Also introduce MMU_NOTIFIER_YOUNG_FAST > to indicate to main mm that doing look-around is likely to be > beneficial. > > If the secondary MMU doesn't support the bitmap, it must return > an int that contains MMU_NOTIFIER_YOUNG_BITMAP_UNRELIABLE. > > [1]: https://lore.kernel.org/all/20230609005935.42390-1-yuzhao@google.com/ > > Suggested-by: Yu Zhao > Signed-off-by: James Houghton > --- > include/linux/mmu_notifier.h | 93 +++++++++++++++++++++++++++++++++--- > include/trace/events/kvm.h | 13 +++-- > mm/mmu_notifier.c | 20 +++++--- > virt/kvm/kvm_main.c | 19 ++++++-- > 4 files changed, 123 insertions(+), 22 deletions(-) > > diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h > index f349e08a9dfe..daaa9db625d3 100644 > --- a/include/linux/mmu_notifier.h > +++ b/include/linux/mmu_notifier.h > @@ -61,6 +61,10 @@ enum mmu_notifier_event { > > #define MMU_NOTIFIER_RANGE_BLOCKABLE (1 << 0) > > +#define MMU_NOTIFIER_YOUNG (1 << 0) > +#define MMU_NOTIFIER_YOUNG_BITMAP_UNRELIABLE (1 << 1) Especially this one really deserves some documentation :) > +#define MMU_NOTIFIER_YOUNG_FAST (1 << 2) And that one as well. Likely best to briefly document all of them, and how they are supposed to be used (return value for X). > + > struct mmu_notifier_ops { > /* > * Called either by mmu_notifier_unregister or when the mm is > @@ -106,21 +110,36 @@ struct mmu_notifier_ops { > * clear_young is a lightweight version of clear_flush_young. Like the > * latter, it is supposed to test-and-clear the young/accessed bitflag > * in the secondary pte, but it may omit flushing the secondary tlb. > + * > + * If @bitmap is given but is not supported, return > + * MMU_NOTIFIER_YOUNG_BITMAP_UNRELIABLE. > + * > + * If the walk is done "quickly" and there were young PTEs, > + * MMU_NOTIFIER_YOUNG_FAST is returned. > */ > int (*clear_young)(struct mmu_notifier *subscription, > struct mm_struct *mm, > unsigned long start, > - unsigned long end); > + unsigned long end, > + unsigned long *bitmap); > > /* > * test_young is called to check the young/accessed bitflag in > * the secondary pte. This is used to know if the page is > * frequently used without actually clearing the flag or tearing > * down the secondary mapping on the page. > + * > + * If @bitmap is given but is not supported, return > + * MMU_NOTIFIER_YOUNG_BITMAP_UNRELIABLE. > + * > + * If the walk is done "quickly" and there were young PTEs, > + * MMU_NOTIFIER_YOUNG_FAST is returned. > */ > int (*test_young)(struct mmu_notifier *subscription, > struct mm_struct *mm, > - unsigned long address); > + unsigned long start, > + unsigned long end, > + unsigned long *bitmap); What does "quickly" mean (why not use "fast")? What are the semantics, I don't find any existing usage of that in this file. Further, what is MMU_NOTIFIER_YOUNG you introduce used for? -- Cheers, David / dhildenb