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[2003:cb:c737:1f00:94ff:246b:30d0:686b]) by smtp.gmail.com with ESMTPSA id b8-20020a5d45c8000000b0033e7715bafasm9429944wrs.59.2024.03.18.03.15.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Mar 2024 03:15:49 -0700 (PDT) Message-ID: <8e13bce5-e353-4258-9891-97158b8ccd84@redhat.com> Date: Mon, 18 Mar 2024 11:15:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2] mm: support multi-size THP numa balancing To: Baolin Wang , "Huang, Ying" Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, wangkefeng.wang@huawei.com, jhubbard@nvidia.com, 21cnbao@gmail.com, ryan.roberts@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <903bf13fc3e68b8dc1f256570d78b55b2dd9c96f.1710493587.git.baolin.wang@linux.alibaba.com> <871q88vzc4.fsf@yhuang6-desk2.ccr.corp.intel.com> <3bf2c3e1-44fd-4bc8-a97b-9da7b606aec0@linux.alibaba.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: <3bf2c3e1-44fd-4bc8-a97b-9da7b606aec0@linux.alibaba.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-Queue-Id: 97CE040015 X-Rspam-User: X-Stat-Signature: cixhsebsa8sjrgqq75y1zamuqrfpwmh3 X-Rspamd-Server: rspam03 X-HE-Tag: 1710756955-503845 X-HE-Meta: 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 PsrOQ0Dc FXioBbE6OiL8xndJU5ulLxzIKOGBFM3XctULsiY1lIq7YkWihwQpk+kyTc+0zSgSzu5dKWPcEYmACLbv0K+JdSrLvE7WdOIxvQUUFcOW/ypreQpfPAZVTrjauhKlLTikS8VRc3uSD3eRJxsBYisb5gmEFShR5bY7hYrKgw6kc8LQGBQ9BKT4rgG20BrFwZc2XAMYmgCtmDBQ0ayujGf6XtRQe70nXobOtev+fKtVUh/YGM/uXtIY9WU76ABbBWFW0jC9G89rYmGCE/qbF9AUd2G2IaR1utE28o1D/K7FvOX6/np+tAkVpgNrwlbaBxwCRJG+CfQzR/uMOhpzpLO0Os8SUy9VrFaNPvFBD9h+XMD9h4TCt+0FVEPx5zU54Osn++sTXr7Ni5rR411v10eVYB0ckjcC+/b69BF090h11gftY6GbJqg9NXnhRbQ39KQeS7Ad6B4VkYkMq+NnaIkZvWdrqVg== 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 18.03.24 11:13, Baolin Wang wrote: > > > On 2024/3/18 17:48, David Hildenbrand wrote: >> On 18.03.24 10:42, Baolin Wang wrote: >>> >>> >>> On 2024/3/18 14:16, Huang, Ying wrote: >>>> Baolin Wang writes: >>>> >>>>> Now the anonymous page allocation already supports multi-size THP >>>>> (mTHP), >>>>> but the numa balancing still prohibits mTHP migration even though it >>>>> is an >>>>> exclusive mapping, which is unreasonable. Thus let's support the >>>>> exclusive >>>>> mTHP numa balancing firstly. >>>>> >>>>> Allow scanning mTHP: >>>>> Commit 859d4adc3415 ("mm: numa: do not trap faults on shared data >>>>> section >>>>> pages") skips shared CoW pages' NUMA page migration to avoid shared >>>>> data >>>>> segment migration. In addition, commit 80d47f5de5e3 ("mm: don't try to >>>>> NUMA-migrate COW pages that have other uses") change to use >>>>> page_count() >>>>> to avoid GUP pages migration, that will also skip the mTHP numa >>>>> scaning. >>>>> Theoretically, we can use folio_maybe_dma_pinned() to detect the GUP >>>>> issue, although there is still a GUP race, the issue seems to have been >>>>> resolved by commit 80d47f5de5e3. Meanwhile, use the >>>>> folio_estimated_sharers() >>>>> to skip shared CoW pages though this is not a precise sharers count. To >>>>> check if the folio is shared, ideally we want to make sure every >>>>> page is >>>>> mapped to the same process, but doing that seems expensive and using >>>>> the estimated mapcount seems can work when running autonuma benchmark. >>>>> >>>>> Allow migrating mTHP: >>>>> As mentioned in the previous thread[1], large folios are more >>>>> susceptible >>>>> to false sharing issues, leading to pages ping-pong back and forth >>>>> during >>>>> numa balancing, which is currently hard to resolve. Therefore, as a >>>>> start to >>>>> support mTHP numa balancing, only exclusive mappings are allowed to >>>>> perform >>>>> numa migration to avoid the false sharing issues with large folios. >>>>> Similarly, >>>>> use the estimated mapcount to skip shared mappings, which seems can >>>>> work >>>>> in most cases (?), and we've used folio_estimated_sharers() to skip >>>>> shared >>>>> mappings in migrate_misplaced_folio() for numa balancing, seems no real >>>>> complaints. >>>> >>>> IIUC, folio_estimated_sharers() cannot identify multi-thread >>>> applications.  If some mTHP is shared by multiple threads in one >>> >>> Right. >>> >> >> Wasn't this "false sharing" previously raised/described by Mel in this >> context? > > Yes, I got confused with the process's false sharing. > >>>> process, how to deal with that? >>> >>> IMHO, seems the should_numa_migrate_memory() already did something to >>> help? >>> >>> ...... >>>     if (!cpupid_pid_unset(last_cpupid) && >>>                 cpupid_to_nid(last_cpupid) != dst_nid) >>>         return false; >>> >>>     /* Always allow migrate on private faults */ >>>     if (cpupid_match_pid(p, last_cpupid)) >>>         return true; >>> ...... >>> >>> If the node of the CPU that accessed the mTHP last time is different >>> from this time, which means there is some contention for that mTHP among >>> threads. So it will not allow migration. >>> >>> If the contention for the mTHP among threads is light or the accessing >>> is relatively stable, then we can allow migration? >>> >>>> For example, I think that we should avoid to migrate on the first fault >>>> for mTHP in should_numa_migrate_memory(). >>>> >>>> More thoughts?  Can we add a field in struct folio for mTHP to count >>>> hint page faults from the same node? >>> >>> IIUC, we do not need add a new field for folio, seems we can reuse >>> ->_flags_2a field. But how to use it? If there are multiple consecutive >>> NUMA faults from the same node, then allow migration? >> >> _flags_2a cannot be used. You could place something after _deferred_list > > Could you be more explicit? I didn't see _flags_2 currently being used, > did I miss something? Yes, that we use it implicitly via page->flags on subpages (for example, some flags are still per-subpage and not per-folio). -- Cheers, David / dhildenb