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[2003:cb:c714:1600:f3b:67cc:3b88:620e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-434aa7644c3sm48705575e9.13.2024.11.28.02.23.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Nov 2024 02:23:00 -0800 (PST) Message-ID: Date: Thu, 28 Nov 2024 11:22:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/4] Add support for File Based Memory Management To: Lorenzo Stoakes , Bijan Tabatabai Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, btabatabai@wisc.edu, akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, mingo@redhat.com, Liam Howlett , Vlastimil Babka , Jann Horn References: <20241122203830.2381905-1-btabatabai@wisc.edu> 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-MFC-PROC-ID: HGifPnb6P4LYI6gPF6WMr47fqHwC9PMdDg8VW2IL6TQ_1732789381 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D917BC0002 X-Rspam-User: X-Stat-Signature: 7iibzarwn3qhjf7x97jr8a94penq5ynd X-HE-Tag: 1732789381-795011 X-HE-Meta: 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 zcbeZz1Q l/nMMTpKYGRbnQJhSdM6kZDQrQ986kH+d8r2G6wvejvCp7r4aBsLapjaahbfjNFqC7qRRUDGA/AQXZkFK/bvYl5ImG6uZ/pWEY5uE1fwSM87w1Pjy70ZHzzp9xyVIk/bGP6EVf8/Tu2FVnFSvvQ8s+5dyQnRUc40TmtvSRJdElunBs5ZojN9C3FBbnTQF8q0hbc0acg0B+C63K+FiXSWs89OYKmhVuJbx71XR01OnODaqw6XrRnja3n6ps/K2oeoDCReTUczT7k/oZ+Iy2qfWy9EeWag/A9RaaSyhWkEkzMNUWfhJl4ChsXDqzb/ks1u/pPbleu0N9Ath1+R014YDFgtOKevHOOiLCCMK+4SiBD8oAZaOIh0W53ChOfUeeD2JfVi9OPfiUNcd9jScKodgL9CgbQ== 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 23.11.24 13:23, Lorenzo Stoakes wrote: > + VMA guys, it's important to run scripts/get_maintainers.pl on your > changes so the right people are pinged :) > > On Fri, Nov 22, 2024 at 02:38:26PM -0600, Bijan Tabatabai wrote: >> This patch set implements file based memory management (FBMM) [1], a >> research project from the University of Wisconsin-Madison where a process's >> memory can be transparently managed by memory managers which are written as >> filesystems. When using FBMM, instead of using the traditional anonymous >> memory path, a process's memory is managed by mapping files from a memory >> management filesystem (MFS) into its address space. The MFS implements the >> memory management related callback functions provided by the VFS to >> implement the desired memory management functionality. After presenting >> this work at a conference, a handful of people asked if we were going to >> upstream the work, so we decided to see if the Linux community would be >> interested in this functionality as well. >> > > While it's a cool project, I don't think it's upstreamable in its current > form - it essentially bypasses core mm functionality and 'does mm' > somewhere else (which strikes me, in effect, as the entire purpose of the > series). > > mm is a subsystem that is in constant flux with many assumptions that one > might make about it being changed, which make it wholly unsuited to having > its functionality exported like this. > > So in in effect it, by its nature, has to export internals somewhere else, > and that somewhere else now assumes things about mm that might change at > any point, additionally bypassing a great deal of highly sensitive and > purposeful logic. > > This series also adds a lot of if (fbmm) { ... } changes to core logic > which is really not how we want to do things. hugetlbfs does this kind of > thing, but it is more or less universally seen as a _bad thing_ and > something we are trying to refactor. > > So any upstreamable form of this would need to a. be part of mm, b. use > existing extensible mechanisms or create them, and c. not have _core_ mm > tasks or activities be performed 'elsewhere'. > > Sadly I think the latter part may make a refactoring in this direction > infeasible, as it seems to me this is sort of the point of this. > > This also means it's not acceptable to export highly sensitive mm internals > as you do in patch 3/4. Certainly in 1/4, as a co-maintainer of the mmap > logic, I can't accept the changes you suggest to brk() and mmap(), sorry. > > There are huge subtleties in much of mm, including very very sensitive lock > mechanisms, and keeping such things within mm means we can have confidence > they work, and that fixes resolve issues. > > I hope this isn't too discouraging, the fact you got this functioning is > amazing and as an out-of-tree research and experimentation project it looks > really cool, but for me, I don't think this is for upstream. I agreed with this sentiment. It looks like something a research OS might want to consider as it's way of dealing with anonymous memory in general, but nothing on squeezes into an existing MM implementation. I'm also not 100% sure on statements like "Providing this transparency" -- what about fork() and COW? What about memory statistics? "Transparency" is a strong word :) -- Cheers, David / dhildenb