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[2003:cb:c70f:2b00:f928:47d8:c9be:9d87]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42ac516252asm16475245e9.26.2024.08.22.01.39.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 Aug 2024 01:39:11 -0700 (PDT) Message-ID: Date: Thu, 22 Aug 2024 10:39:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 0/4] mm: clarify nofail memory allocation To: Michal Hocko , Barry Song <21cnbao@gmail.com> Cc: Linus Torvalds , Yafang Shao , akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev References: <20240817062449.21164-1-21cnbao@gmail.com> <7050deab-e99c-4c83-b7b9-b5dad42f4e95@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-Stat-Signature: tbrtou9s7r65kn3xu1dmkkjpg1tkq4pk X-Rspamd-Queue-Id: CCF6C4001D X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1724315955-686905 X-HE-Meta: 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 EiH2eoN5 aCEE36JDv8zLW0tvgDs6J3WLdMavQKSxy1InwpW4M4yK+h4WXeM+JQbY+v7S/Vj3NYzHmogd4zn463n5N8LT8G4yx6HauBtxjNylDhAQm1w3JFW0AijmZcOVnQ6demfVdEZTn8M9SNexeJJNxjt4j2YeH6MFP+OYM2pyKRmDGKlQ0to8QoY542X3FZ2dGiHz4IbHKM7RQ78Ks345PPvhJQpM7JKv6ON3JmLld/ibs1oVv3GsuZ1oK/PIdAoVPwFi5GEoDJijr0c4a0EMpitN5PTrXXffAMJZirFavW+F1WCm7Bn2i0FPEB8lnnzN/5e6WZVpP9iwfQ/zg0Va+qXEm4RIgVQaPbsrlsB3BbUMlH1492Qey8k7U52y4cFokS0awFWqx7lYceYZVVvZ45vHKkrav6G8Aqduq+r/JV2bSZ0hRjQy3dfdx2zNXU/yJB1B+CMAU 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 22.08.24 10:24, Michal Hocko wrote: > On Thu 22-08-24 19:57:41, Barry Song wrote: >> Regarding the concern about 'leaving locks >> behind' you have in that subthread, I believe there's no difference >> when returning NULL, as it could still leave locks behind but offers >> a chance for the calling process to avoid an immediate crash. > > Yes, I have mentioned this risk just for completeness. Without having > some sort of unwinding mechanism we are doomed to not be able to handle > this. > > The sole difference between just returning NULL and OOPsing rigth away > is that the former is not guaranteed to happen and the caller can cause > an actual harm by derefering non-oopsing addressed close to 0 which > would be a) much harder to find out b) could cause much more damage than > killing the context right away. > > Besides that I believe we have many BUG_ON users which would really > prefer to just call the current context instead, they just do not have > means to do that so OOPS_ON could be a safer way to stop bad users and > reduce the number of BUG_ONs as well. To me that sounds better as well, but I was also wondering if it's easy to implement or easy to assemble from existing pieces. Linus has a point that "retry forever" can also be nasty. I think the important part here is, though, that we report sufficient information (stacktrace), such that the problem can be debugged reasonably well, and not just having a locked-up system. But then the question is: does it really make sense to differentiate difference between an NOFAIL allocation under memory pressure of MAX_ORDER compared to MAX_ORDER+1 (Linus also touched on that)? It could well take minutes/hours/days to satisfy a very large NOFAIL allocation. So callers should be prepared to run into effective lockups ... :/ NOFAIL shouldn't exist, or at least not used to that degree. I am to blame myself, I made use of it in kernel/resource.c, where there is no turning back when completed memory unplug to 99% (even having freed the vmemmap), but then we might have to allocate a new node in the resource tree, when having to split an existing one. Maybe there would be ways to preallocate before starting memory unplug, or to pre-split ... But then again, sizeof(struct resource) is probably so small that it likely would never fail. -- Cheers, David / dhildenb