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[91.12.99.100]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4256b0c19eesm208322605e9.45.2024.07.02.08.38.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Jul 2024 08:38:18 -0700 (PDT) Message-ID: <686d3f32-45b0-4dd5-8954-e75748b9c946@redhat.com> Date: Tue, 2 Jul 2024 17:38:17 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm: Fix khugepaged activation policy To: Ryan Roberts , Andrew Morton , Jonathan Corbet , Barry Song , Baolin Wang , Lance Yang , Yang Shi Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20240702144617.2291480-1-ryan.roberts@arm.com> Content-Language: en-US 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 02.07.24 17:29, Ryan Roberts wrote: > On 02/07/2024 15:57, David Hildenbrand wrote: >> On 02.07.24 16:46, Ryan Roberts wrote: >>> Since the introduction of mTHP, the docuementation has stated that >>> khugepaged would be enabled when any mTHP size is enabled, and disabled >>> when all mTHP sizes are disabled. There are 2 problems with this; 1. >>> this is not what was implemented by the code and 2. this is not the >>> desirable behavior. >>> >>> Desirable behavior is for khugepaged to be enabled when any PMD-sized >>> THP is enabled, anon or file. (Note that file THP is still controlled by >>> the top-level control so we must always consider that, as well as the >>> PMD-size mTHP control for anon). khugepaged only supports collapsing to >>> PMD-sized THP so there is no value in enabling it when PMD-sized THP is >>> disabled. So let's change the code and documentation to reflect this >>> policy. >>> >>> Further, per-size enabled control modification events were not >>> previously forwarded to khugepaged to give it an opportunity to start or >>> stop. Consequently the following was resulting in khugepaged eroneously >>> not being activated: >>> >>>    echo never > /sys/kernel/mm/transparent_hugepage/enabled >>>    echo always > /sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled >>> >>> Signed-off-by: Ryan Roberts >>> Fixes: 3485b88390b0 ("mm: thp: introduce multi-size THP sysfs interface") >>> Closes: >>> https://lore.kernel.org/linux-mm/7a0bbe69-1e3d-4263-b206-da007791a5c4@redhat.com/ >>> Cc: stable@vger.kernel.org >>> --- >>> >>> Hi All, >>> >>> Applies on top of today's mm-unstable (9bb8753acdd8). No regressions observed in >>> mm selftests. >>> >>> When fixing this I also noticed that khugepaged doesn't get (and never has been) >>> activated/deactivated by `shmem_enabled=`. I'm not sure if khugepaged knows how >>> to collapse shmem - perhaps it should be activated in this case? >>> >> >> Call me confused. >> >> khugepaged_scan_mm_slot() and madvise_collapse() only all >> hpage_collapse_scan_file() with ... IS_ENABLED(CONFIG_SHMEM) ? > > Looks like khugepaged_scan_mm_slot() was converted from: > > if (shmem_file(vma->vm_file)) { > > to: > > if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { > > By 99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 which adds THP collapse support for > non-shmem files. Clearly that looks wrong, but I guess never spotted in practice > because noone disables shemem? > > I guess madvise_collapse() was a copy/paste? > Likely. >> >> collapse_file() is only called by hpage_collapse_scan_file() ... and there we >> check "shmem_file(file)". >> >> So why is the IS_ENABLED(CONFIG_SHMEM) check in there if collapse_file() seems >> to "collapse filemap/tmpfs/shmem pages into huge one". >> >> Anyhow, we certainly can collapse shmem (that's how it all started IIUC). > > Yes, thanks for pointing me at it. Should have just searched "shmem" in > khugepaged.c :-/ > >> >> Besides that, khugepaged only seems to collapse !shmem with >>   VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); > > That makes sense. I guess I could use IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) to > tighen the (non-shmem) file THP check in hugepage_pmd_enabled() (currently I'm > unconditionally using the top-level enabled setting as a "is THP enabled for > files" check). > > But back to my original question, I think hugepage_pmd_enabled() should also be > explicitly checking the appropriate shmem_enabled controls and ORing in the > result? Otherwise in a situation where only shmem is THP enabled (and file/anon > THP is disabled) khugepaged won't run. I think so. > >> >> The thp_vma_allowable_order() check tests if we are allowed to collapse a >> PMD_ORDER in that VMA. > > I don't follow the relevance of this statement. On whatever VMA we indicate true, we will try to collapse in khugepaged. Regarding the question, what khugepaged will try to collapse. -- Cheers, David / dhildenb