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[2003:cb:c740:2200:95d8:cbf4:fffd:7f81]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-422f6419e38sm167784235e9.39.2024.06.17.10.49.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Jun 2024 10:49:41 -0700 (PDT) Message-ID: <86b29391-ad2a-4c4b-b9a8-974d1876632c@redhat.com> Date: Mon, 17 Jun 2024 19:49:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/3] asynchronously scan and free empty user PTE pages To: Qi Zheng Cc: hughd@google.com, willy@infradead.org, mgorman@suse.de, muchun.song@linux.dev, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <02f8cbd0-8b2b-4c2d-ad96-f854d25bf3c2@redhat.com> <2cda0af6-8fde-4093-b615-7979744d6898@redhat.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: 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 X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 1B69140018 X-Stat-Signature: fuwwggg8aa8pm4m8bbkpq4ormnbsbw6h X-HE-Tag: 1718646585-556878 X-HE-Meta: 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 gVD4Z08N QLiKklyF1bR0d5BcqE8VsunXukkrLOhy3pqjghXJ6l8ZLVnhiBI4tsCeRRkjTOo/2svv7UtFVleSRDVyYILDrxoRRLktjVXatmCFbjBQzwyh4KgLrveKp3wKH3NTMsMetHYlmt1TKrQiuJZ4EVgsJT7L1Hf9TuoA10I30N734eSpto8wZnamO+J68OMfZLCQaAHS7SJBfEoArnJ0bC8WxDp3N3mE+eWGYo215YfwCs//7LquXGxYGKYZnfPY3faD3+eGwQiU6nIm02vDGlM+1c87ed8RwAyrKCPStJcBFxI9h05CWbOehwTJvbTH2tSSL+ddS0OlROW+OUvwUw/oChKeOHttkrT1ifanyJOAEY4sFRKovXFgU1ndf8JoYhHFLTbhn3VuNbhOJ3x7Xj/p+yzc3ET/JcJ/blGjshr2D8EDLmUnVVUH5Q4XyYNTDOxrYiPkhBqaPOydvn6U3+AAgPPJA/w== 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: >> >> No strong opinion, something synchronous sounds to me like the >> low-hanging fruit, that could add the infrastructure to be used by >> something more advanced/synchronously :) > > Got it, I will try to do the following in the next version. > > a. for MADV_DONTNEED case, try synchronous reclaim as you said > I think that really is the low hanging fruit that would cover quite some cases already: (1) reclaim when MADV_DONTNEED spans the complete page table. Then, there is (2) reclaim when MADV_DONTNEED spans only part of the page table (e.g., single PTE), but my best guess is that it's better to scan for that asynchronously than making possibly each MADV_DONTNEED sycall invocation slower. (1) would already help a lot and showcase how the locking/machinery would work. > b. for MADV_FREE case: > > - add a madvise option for synchronous reclaim > > - add another madvise option to mark the vma, then add its > corresponding mm to a global list, and then traverse > the list and reclaim it when the memory is tight and > enters the system reclaim path. > (maybe there is an option to unmark) > > c. for s390 case you mentioned, create a CONFIG_FREE_PT first, and > then s390 will not select this config until the problem is solved. > > d. for lockless scan, try using disabling IRQ or (mmap read lock + > pte_offset_map_nolock). Although d) really only is desired when scanning asynchronously I think. During (1) above, we know that the table will be very likely empty (unless weird race). -- Cheers, David / dhildenb