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[2003:cb:c719:8200:487a:3426:a17e:d7b7]) by smtp.gmail.com with ESMTPSA id n5-20020a05600c3b8500b0041a3b5ed993sm14584205wms.25.2024.04.25.00.19.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Apr 2024 00:19:19 -0700 (PDT) Message-ID: Date: Thu, 25 Apr 2024 09:19:18 +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: Zi Yan , linux-mm@kvack.org Cc: Andrew Morton , "Matthew Wilcox (Oracle)" , Yang Shi , Ryan Roberts , Barry Song <21cnbao@gmail.com>, Lance Yang , 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: <20240424224614.477221-1-zi.yan@sent.com> 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-Rspamd-Queue-Id: E8871140002 X-Stat-Signature: zh8d84hen655cxqroo9tdcd5bozp9a7d X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1714029565-572540 X-HE-Meta: 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 6N5M6pB6 H6KkqhVSf4L93eWB4yCYt0uhKPjWJMZxoWGvzmH29aXkvN8G2C2xVV4KVPuhKJ+dzoIX/sDiZXVRfLs62oHTkASZT3Zh5HPMbmhluB0fYZyuLUG+MY1lB8ihNjmd9KGVrbB8CkJIUIaMmDpdfdetgvJWIS7xX6onotmiN4iEoCZE3HQ2//heqFrxfLavuU667uRnN42YVt/g0JONB5hHZMeKWnBso4rXzsraS/P02WbYzBnCbJ6m4ZDOguWXeTcuiF7uUpZQY6vFVSAkmSNyZlts4suMBT7+jshuJsCUXIXmxeHjWI4bl3FM3lvTnLg+lzNk4+MnlpMbFsWK9hmgegbI4f1mwhp+5sf2e4C+Twebx05zEVwewxEf7qVfhYCIMPJR9I+FGnYxKBRp/U1k0T1vYBFq6R2FBcr+u08pBZUqd4yx6IYhN/8y4mDITnraO4Lgm7nVyW1nGhGlYrmusn/zQYw== 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 00:46, 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 > 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 Once again: your patch won't fix it either. > 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. It will still be present. Just less frequently. > > 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))) > + deferred_split_folio(folio); Please refrain from posting a new patch before the discussion on the old one is done. See my comments on v2 why optimizing out the function call is a reasonable thing to do *where we cannot batch* and the misaccounting will still happen. But it can be done independently. -- Cheers, David / dhildenb