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[2003:cb:c709:3400:5126:3051:d630:92ee]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3675a0d8ed0sm15514574f8f.28.2024.07.03.03.11.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Jul 2024 03:11:27 -0700 (PDT) Message-ID: <79910a02-7767-4f70-9248-319aba79fb45@redhat.com> Date: Wed, 3 Jul 2024 12:11:26 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] kpageflags: fix wrong KPF_THP on non-pmd-mappable compound pages To: ran xiaokai Cc: akpm@linux-foundation.org, baohua@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterx@redhat.com, ran.xiaokai@zte.com.cn, ryan.roberts@arm.com, svetly.todorov@memverge.com, vbabka@suse.cz, willy@infradead.org, ziy@nvidia.com References: <1fddf73d-577f-4b4c-996a-818dd99eb489@redhat.com> <20240703092023.76749-1-ranxiaokai627@163.com> From: David Hildenbrand Content-Language: en-US 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: <20240703092023.76749-1-ranxiaokai627@163.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 03.07.24 11:20, ran xiaokai wrote: >> On 26.06.24 04:49, ran xiaokai wrote: >>> From: Ran Xiaokai >>> >>> KPF_COMPOUND_HEAD and KPF_COMPOUND_TAIL are set on "common" compound >>> pages, which means of any order, but KPF_THP should only be set >>> when the folio is a 2M pmd mappable THP. Since commit 19eaf44954df >> >> "should only be set" -- who says that? :) >> >> The documentation only talks about "Contiguous pages which construct >> transparent hugepages". Sure, when it was added there were only PMD ones. >> >> >>> ("mm: thp: support allocation of anonymous multi-size THP"), >>> multiple orders of folios can be allocated and mapped to userspace, >>> so the folio_test_large() check is not sufficient here, >>> replace it with folio_test_pmd_mappable() to fix this. >>> >> >> A couple of points: >> >> 1) If I am not daydreaming, ever since we supported non-PMD THP in the >> pagecache (much longer than anon mTHP), we already indicate KPF_THP >> for them here. So this is not anon specific? Or am I getting the >> PG_lru check all wrong? >> >> 2) Anon THP are disabled as default. If some custom tool cannot deal >> with that "extension" we did with smaller THP, it shall be updated if >> it really has to special-case PMD-mapped THP, before enabled by the >> admin. >> >> >> I think this interface does exactly what we want, as it is right now. >> Unless there is *good* reason, we should keep it like that. >> >> So I suggest >> >> a) Extend the documentation to just state "THP of any size and any >> mapping granularity" or sth like that. >> >> b) Maybe using folio_test_large_rmappable() instead of "(k & (1 << >> PG_lru)) || is_anon", so even isolated-from-LRU THPs are indicated >> properly. > > Hi, David, > > The "is_anon" check was introduced to also include page vector cache > pages, but now large folios are added to lru list directly, bypassed > the pagevec cache. So the is_anon check seems unnecessary here. > As now pagecache also supports large folios, the is_anon check seems > unsufficient here. > > Can i say that for userspace memory, > folio_test_large_rmappable() == folio_test_large()? > if that is true, except the "if ((k & (1 << PG_lru)) || is_anon)" > check, we can also remove the folio_test_large() check, > like this: > > else if (folio_test_large_rmappable(folio)) { > u |= 1 << KPF_THP; > else if (is_huge_zero_folio(folio)) { > u |= 1 << KPF_ZERO_PAGE; > u |= 1 << KPF_THP; > } > } else if (is_zero_pfn(page_to_pfn(page))) > > This will also include the isolated folios. You'll have to keep the folio_test_large() check, folio_test_large_rmappable() wants us to check that ahead of time. Something like ... else if (folio_test_large(folio) && folio_test_large_rmappable(folio)) { /* Note: we indicate any THPs here, not just PMD-sized ones */ u |= 1 << KPF_THP; } else if (is_huge_zero_folio(folio)) { u |= 1 << KPF_ZERO_PAGE; u |= 1 << KPF_THP } else if (is_zero_pfn(page_to_pfn(page))) { u |= 1 << KPF_ZERO_PAGE; } Would likely work and keep the existing behavior (+ include isolated ones). -- Cheers, David / dhildenb