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[2003:cb:c70b:b700:5a87:3a7a:c28d:2cff]) by smtp.gmail.com with ESMTPSA id f12-20020adfb60c000000b00336b8461a5esm2240280wre.88.2024.01.17.10.41.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Jan 2024 10:41:05 -0800 (PST) Message-ID: <22b24ce9-d143-4b5f-87da-bf68e4fa46d3@redhat.com> Date: Wed, 17 Jan 2024 19:41:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm/madvise: introduce MADV_TRY_COLLAPSE for attempted synchronous hugepage collapse To: Zach O'Keefe , Lance Yang Cc: akpm@linux-foundation.org, songmuchun@bytedance.com, linux-kernel@vger.kernel.org, Yang Shi , Peter Xu , Michael Knyszek , Minchan Kim , Michal Hocko , linux-mm@kvack.org References: <20240117050217.43610-1-ioworker0@gmail.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: 8bit X-Rspamd-Queue-Id: CD33A1A0020 X-Rspam-User: X-Stat-Signature: kftniqnaa9dq3q9998ib7afqbur5f7qo X-Rspamd-Server: rspam03 X-HE-Tag: 1705516869-285346 X-HE-Meta: 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 2tsANbER 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 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 17.01.24 18:10, Zach O'Keefe wrote: > [+linux-mm & others] > > On Tue, Jan 16, 2024 at 9:02 PM Lance Yang wrote: >> >> This idea was inspired by MADV_COLLAPSE introduced by Zach O'Keefe[1]. >> >> Introduce a new madvise mode, MADV_TRY_COLLAPSE, that allows users to >> make a least-effort attempt at a synchronous collapse of memory at >> their own expense. >> >> The only difference from MADV_COLLAPSE is that the new hugepage allocation >> avoids direct reclaim and/or compaction, quickly failing on allocation errors. >> >> The benefits of this approach are: >> >> * CPU is charged to the process that wants to spend the cycles for the THP >> * Avoid unpredictable timing of khugepaged collapse >> * Prevent unpredictable stalls caused by direct reclaim and/or compaction >> >> Semantics >> >> This call is independent of the system-wide THP sysfs settings, but will >> fail for memory marked VM_NOHUGEPAGE. If the ranges provided span >> multiple VMAs, the semantics of the collapse over each VMA is independent >> from the others. This implies a hugepage cannot cross a VMA boundary. If >> collapse of a given hugepage-aligned/sized region fails, the operation may >> continue to attempt collapsing the remainder of memory specified. >> >> The memory ranges provided must be page-aligned, but are not required to >> be hugepage-aligned. If the memory ranges are not hugepage-aligned, the >> start/end of the range will be clamped to the first/last hugepage-aligned >> address covered by said range. The memory ranges must span at least one >> hugepage-sized region. >> >> All non-resident pages covered by the range will first be >> swapped/faulted-in, before being internally copied onto a freshly >> allocated hugepage. Unmapped pages will have their data directly >> initialized to 0 in the new hugepage. However, for every eligible >> hugepage aligned/sized region to-be collapsed, at least one page must >> currently be backed by memory (a PMD covering the address range must >> already exist). >> >> Allocation for the new hugepage will not enter direct reclaim and/or >> compaction, quickly failing if allocation fails. When the system has >> multiple NUMA nodes, the hugepage will be allocated from the node providing >> the most native pages. This operation operates on the current state of the >> specified process and makes no persistent changes or guarantees on how pages >> will be mapped, constructed, or faulted in the future. >> >> Return Value >> >> If all hugepage-sized/aligned regions covered by the provided range were >> either successfully collapsed, or were already PMD-mapped THPs, this >> operation will be deemed successful. On success, madvise(2) returns 0. >> Else, -1 is returned and errno is set to indicate the error for the >> most-recently attempted hugepage collapse. Note that many failures might >> have occurred, since the operation may continue to collapse in the event a >> single hugepage-sized/aligned region fails. >> >> ENOMEM Memory allocation failed or VMA not found >> EBUSY Memcg charging failed >> EAGAIN Required resource temporarily unavailable. Try again >> might succeed. >> EINVAL Other error: No PMD found, subpage doesn't have Present >> bit set, "Special" page no backed by struct page, VMA >> incorrectly sized, address not page-aligned, ... >> >> Use Cases >> >> An immediate user of this new functionality is the Go runtime heap allocator >> that manages memory in hugepage-sized chunks. In the past, whether it was a >> newly allocated chunk through mmap() or a reused chunk released by >> madvise(MADV_DONTNEED), the allocator attempted to eagerly back memory with >> huge pages using madvise(MADV_HUGEPAGE)[2] and madvise(MADV_COLLAPSE)[3] >> respectively. However, both approaches resulted in performance issues; for >> both scenarios, there could be entries into direct reclaim and/or compaction, >> leading to unpredictable stalls[4]. Now, the allocator can confidently use >> madvise(MADV_TRY_COLLAPSE) to attempt the allocation of huge pages. >> >> [1] https://github.com/torvalds/linux/commit/7d8faaf155454f8798ec56404faca29a82689c77 >> [2] https://github.com/golang/go/commit/8fa9e3beee8b0e6baa7333740996181268b60a3a >> [3] https://github.com/golang/go/commit/9f9bb26880388c5bead158e9eca3be4b3a9bd2af >> [4] https://github.com/golang/go/issues/63334 > > Thanks for the patch, Lance, and thanks for providing the links above, > referring to issues Go has seen. > > I've reached out to the Go team to try and understand their use case, > and how we could help. It's not immediately clear whether a > lighter-weight MADV_COLLAPSE is the answer, but it could turn out to > be. > > That said, with respect to the implementation, should a need for a > lighter-weight MADV_COLLAPSE be warranted, I'd personally like to see > process_madvise(2) be the "v2" of madvise(2), where we can start > leveraging the forward-facing flags argument for these different > advice flavors. We'd need to safely revert v5.10 commit a68a0262abdaa > ("mm/madvise: remove racy mm ownership check") so that > process_madvise(2) can always operate on self. IIRC, this was ~ the > plan we landed on during MADV_COLLAPSE dev discussions (i.e. pick a > sane default, and implement options in flags down the line). +1, using process_madvise() would likely be the right approach. -- Cheers, David / dhildenb