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[2003:cb:c719:8200:487a:3426:a17e:d7b7]) by smtp.gmail.com with ESMTPSA id u17-20020adfeb51000000b00347321735a6sm18992189wrn.66.2024.04.25.00.15.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Apr 2024 00:15:47 -0700 (PDT) Message-ID: <815e2114-f739-4f2f-b09f-a23a2fc3214b@redhat.com> Date: Thu, 25 Apr 2024 09:15:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/rmap: do not add fully unmapped large folio to deferred split list To: Zi Yan , Yang Shi Cc: linux-mm@kvack.org, Andrew Morton , "Matthew Wilcox (Oracle)" , Ryan Roberts , Barry Song <21cnbao@gmail.com>, linux-kernel@vger.kernel.org References: <20240424211031.475756-1-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: rspam03 X-Rspamd-Queue-Id: 83169A0011 X-Stat-Signature: 5cpykue1fizkyzmj8zkxfx8i69tfmmh5 X-Rspam-User: X-HE-Tag: 1714029352-860815 X-HE-Meta: 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 vgp4lOIX bIszHcISHxZhpwN6GZOo8NjncGxp//YKV0xkCI5Z8OnL/tMyt2sZYxViw+Mg6zpMiJ4jZpZWbkFJzgqkRqchLlaCNEdjVSXB2sU+xD1TgfyFH1WouTmAd1UKWceTp+lVtausRm+/a5OMA5cqj5/8x3cRh+dUFon7z27YLcOV4C0nQYT0= 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 00:39, Zi Yan wrote: > On 24 Apr 2024, at 18:32, Yang Shi wrote: > >> On Wed, Apr 24, 2024 at 2:10 PM 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. >>> >>> 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 everything. A fully unmapped PTE-mapped order-9 THP was also 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. >> >> Shall you mention the miscounting for mTHP too? There is another patch >> series adding the counter support for mTHP. > > OK, will add it. I thought I made it clear: this patch won't "fix" it. Misaccounting will still happen. Just less frequently. Please spell that out. >> >>> >>> 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 >>> --- >>> mm/rmap.c | 8 +++++--- >>> 1 file changed, 5 insertions(+), 3 deletions(-) >>> >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index a7913a454028..220ad8a83589 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -1553,9 +1553,11 @@ 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) && >>> + list_empty(&folio->_deferred_list) && >> >> Do we really need this check? deferred_split_folio() does the same >> check too. Bailing out earlier sounds ok too, but there may not be too >> much gain. > > Sure, I can remove it. Please leave it. It's a function call that cannot be optimized out otherwise. -- Cheers, David / dhildenb