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[2003:cb:c719:8200:487a:3426:a17e:d7b7]) by smtp.gmail.com with ESMTPSA id p8-20020a05600c358800b00418f72d9027sm24262026wmq.18.2024.04.25.00.21.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Apr 2024 00:21:08 -0700 (PDT) Message-ID: <5e6bf4c6-c4a5-4be3-b203-ecc77ba4e5d9@redhat.com> Date: Thu, 25 Apr 2024 09:21:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/rmap: do not add fully unmapped large folio to deferred split list To: Lance Yang , Zi Yan Cc: linux-mm@kvack.org, Andrew Morton , "Matthew Wilcox (Oracle)" , Yang Shi , Ryan Roberts , Barry Song <21cnbao@gmail.com>, linux-kernel@vger.kernel.org References: <20240424224614.477221-1-zi.yan@sent.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: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0C6B84000C X-Rspam-User: X-Stat-Signature: rqxjm885fmh9ktab8m7m51ns8zrsd8ay X-HE-Tag: 1714029674-466125 X-HE-Meta: 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 GIPMf+mS 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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 25.04.24 05:45, Lance Yang wrote: > Hey Zi, > > On Thu, Apr 25, 2024 at 6:46 AM Zi Yan wrote: >> >> From: Zi Yan >> >> In __folio_remove_rmap(), a large folio is added to deferred split list >> if any page in a folio loses its final mapping. It is possible that >> the folio is unmapped fully, but it is unnecessary to add the folio > > Agreed. If a folio is fully unmapped, then that's unnecessary to add > to the deferred split list. > >> to deferred split list at all. Fix it by checking folio->_nr_pages_mapped >> before adding a folio to deferred split list. If the folio is already >> on the deferred split list, it will be skipped. This issue applies to >> both PTE-mapped THP and mTHP. >> >> Commit 98046944a159 ("mm: huge_memory: add the missing >> folio_test_pmd_mappable() for THP split statistics") tried to exclude >> mTHP deferred split stats from THP_DEFERRED_SPLIT_PAGE, but it does not >> fix the above issue. A fully unmapped PTE-mapped order-9 THP was still >> added to deferred split list and counted as THP_DEFERRED_SPLIT_PAGE, >> since nr is 512 (non zero), level is RMAP_LEVEL_PTE, and inside >> deferred_split_folio() the order-9 folio is folio_test_pmd_mappable(). >> However, this miscount was present even earlier due to implementation, >> since PTEs are unmapped individually and first PTE unmapping adds the THP >> into the deferred split list. >> >> With commit b06dc281aa99 ("mm/rmap: introduce >> folio_remove_rmap_[pte|ptes|pmd]()"), kernel is able to unmap PTE-mapped >> folios in one shot without causing the miscount, hence this patch. >> >> Signed-off-by: Zi Yan >> Reviewed-by: Yang Shi >> --- >> mm/rmap.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/mm/rmap.c b/mm/rmap.c >> index a7913a454028..2809348add7b 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1553,9 +1553,10 @@ static __always_inline void __folio_remove_rmap(struct folio *folio, >> * page of the folio is unmapped and at least one page >> * is still mapped. >> */ >> - if (folio_test_large(folio) && folio_test_anon(folio)) >> - if (level == RMAP_LEVEL_PTE || nr < nr_pmdmapped) >> - deferred_split_folio(folio); >> + if (folio_test_large(folio) && folio_test_anon(folio) && >> + ((level == RMAP_LEVEL_PTE && atomic_read(mapped)) || >> + (level == RMAP_LEVEL_PMD && nr < nr_pmdmapped))) > > Perhaps we only need to check the mapcount? > > IIUC, if a large folio that was PMD/PTE mapped is fully unmapped here, > then folio_mapcount() will return 0. See discussion on v1. folio_large_mapcount() would achieve the same without another folio_test_large() check, but in the context of this patch it doesn't really matter. -- Cheers, David / dhildenb