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[91.12.107.195]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-41f88110f3esm20824155e9.29.2024.05.08.05.02.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 May 2024 05:02:50 -0700 (PDT) Message-ID: <928c73de-76b0-40d6-a0c3-23d72270ac5c@redhat.com> Date: Wed, 8 May 2024 14:02:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 5/8] mm: shmem: add multi-size THP sysfs interface for anonymous shmem To: Ryan Roberts , Baolin Wang , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com, shy828301@gmail.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <6b4afed1ef26dbd08ae9ec58449b329564dcef3e.1714978902.git.baolin.wang@linux.alibaba.com> <30329a82-45b9-4e78-8c48-bd56af113786@arm.com> <0b3735bc-2ad7-44f8-808b-37fc90d57199@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: 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: y9x4ye4dei6j6wgbp1ghpo17bhc71hwr X-Rspam-User: X-Rspamd-Queue-Id: 5559E20016 X-Rspamd-Server: rspam05 X-HE-Tag: 1715169776-893766 X-HE-Meta: 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 VeDCfNe/ 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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 08.05.24 11:02, Ryan Roberts wrote: > On 08/05/2024 08:12, David Hildenbrand wrote: >> On 08.05.24 09:08, David Hildenbrand wrote: >>> On 08.05.24 06:45, Baolin Wang wrote: >>>> >>>> >>>> On 2024/5/7 18:52, Ryan Roberts wrote: >>>>> On 06/05/2024 09:46, Baolin Wang wrote: >>>>>> To support the use of mTHP with anonymous shmem, add a new sysfs interface >>>>>> 'shmem_enabled' in the '/sys/kernel/mm/transparent_hugepage/hugepages-kB/' >>>>>> directory for each mTHP to control whether shmem is enabled for that mTHP, >>>>>> with a value similar to the top level 'shmem_enabled', which can be set to: >>>>>> "always", "inherit (to inherit the top level setting)", "within_size", >>>>>> "advise", >>>>>> "never", "deny", "force". These values follow the same semantics as the top >>>>>> level, except the 'deny' is equivalent to 'never', and 'force' is equivalent >>>>>> to 'always' to keep compatibility. >>>>> >>>>> We decided at [1] to not allow 'force' for non-PMD-sizes. >>>>> >>>>> [1] >>>>> https://lore.kernel.org/linux-mm/533f37e9-81bf-4fa2-9b72-12cdcb1edb3f@redhat.com/ >>>>> >>>>> However, thinking about this a bit more, I wonder if the decision we made to >>>>> allow all hugepages-xxkB/enabled controls to take "inherit" was the wrong one. >>>>> Perhaps we should have only allowed the PMD-sized enable=inherit (this is just >>>>> for legacy back compat after all, I don't think there is any use case where >>>>> changing multiple mTHP size controls atomically is actually useful). Applying >>>> >>>> Agree. This is also our usage of 'inherit'. >> >> Missed that one: there might be use cases in the future once we would start >> defaulting to "inherit" for all knobs (a distro might default to that) and >> default-enable THP in the global knob. Then, it would be easy to disable any THP >> by disabling the global knob. (I think that's the future we're heading to, where >> we'd have an "auto" mode that can be set on the global toggle). >> >> But I am just making up use cases ;) I think it will be valuable and just doing >> it consistently now might be cleaner. > > I agree that consistency between enabled and shmem_enabled is top priority. And > yes, I had forgotten about the glorious "auto" future. So probably continuing > all sizes to select "inherit" is best. > > But for shmem_enabled, that means we need the following error checking: > > - It is an error to set "force" for any size except PMD-size > > - It is an error to set "force" for the global control if any size except PMD- > size is set to "inherit" > > - It is an error to set "inherit" for any size except PMD-size if the global > control is set to "force". > > Certainly not too difficult to code and prove to be correct, but not the nicest > UX from the user's point of view when they start seeing errors. > > I think we previously said this would likely be temporary, and if/when tmpfs > gets mTHP support, we could simplify and allow all sizes to be set to "force". > But I wonder if tmpfs would ever need explicit mTHP control? Maybe it would be > more suited to the approach the page cache takes to transparently ramp up the > folio size as it faults more in. (Just saying there is a chance that this error > checking becomes permanent). Note that with shmem you're inherently facing the same memory waste issues etc as you would with anonymous memory. (sometimes even worse, if you're running shmem that's configured to be unswappable!). -- Cheers, David / dhildenb