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[2003:cb:c705:1400:78ba:c2d2:22a1:8858]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-360750ad2cdsm13775162f8f.61.2024.06.18.02.40.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Jun 2024 02:40:52 -0700 (PDT) Message-ID: <4f56d1e9-2c23-42e5-9aef-6b29d072138e@redhat.com> Date: Tue, 18 Jun 2024 11:40:51 +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> <86b29391-ad2a-4c4b-b9a8-974d1876632c@redhat.com> <025ea89a-bb94-4f60-b6ad-d8b88d3cfc60@bytedance.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: <025ea89a-bb94-4f60-b6ad-d8b88d3cfc60@bytedance.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: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E93D1100020 X-Stat-Signature: rwrsxoudt75j4hihpxxb3g99xzxkm5qb X-Rspam-User: X-HE-Tag: 1718703661-880364 X-HE-Meta: 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 6PvvP/zM WT/u20WnaJJzP5tky8WCghg/utgvvIsbaUaXH2t1rKhuOz+evGiMCq9ZWiPqmc8W8x3opc27fRnrcaAvZQTuQTob26inSRy/ldO/HjPdS4YlLk9l0WwQWTzgqGGc6AFp819gilDie2pFFGnwK/8eDke0PUwGvI1QXloAhu0Y+xZxphCB9kg2k1lHW+4N9lLrPMsZJMxMOhtfaBg0H1tjsmhJAF2tNAS/2BfzkNB7hyTspZXuz83Ly/iZ5Gz3GElfM8xJGaMqK6NtLn+utmVNIQ/VXpikiYRFV9rOu2wcQBA86jCFSq6m5+1HgMu0xdYbP9BH7Iah3FyxDwtfbmcer9im+XWnBJznhlJR1zSvRN8v6hWw134LIkWS0DfFvI2Ry3X7CRY0paW41Afw= 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 18.06.24 09:51, Qi Zheng wrote: > Hi David, > > On 2024/6/18 01:49, David Hildenbrand wrote: >> >>>> >>>> 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. > > I will check and free the PTE page in the zap_pte_range() if the > (end - addr >= PMD_SIZE) condition is met. > >> >> 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. > > Maybe just mark the vma, and then scan it in the system reclaim path. > > I also plan to do this in the MADV_FREE case, instead of adding an > asynchronous madvise option first. > >> >> (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). > > Agree. Again, thanks for working on this. Let me know (can also do privately) if you run into any issues or think I can be of help. :) -- Cheers, David / dhildenb