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[2003:cb:c72f:f700:104b:9184:1b45:1898]) by smtp.gmail.com with ESMTPSA id r1-20020a05600c35c100b0041228b2e179sm8357026wmq.39.2024.02.26.05.50.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 26 Feb 2024 05:50:27 -0800 (PST) Message-ID: Date: Mon, 26 Feb 2024 14:50:26 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] madvise:madvise_cold_or_pageout_pte_range(): allow split while folio_estimated_sharers = 0 To: Ryan Roberts , Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Barry Song , Yin Fengwei , Yu Zhao , Kefeng Wang , Matthew Wilcox , Minchan Kim , Vishal Moola , Yang Shi References: <20240221085036.105621-1-21cnbao@gmail.com> <71fa4302-2df6-4e55-a5a8-7609476c41d4@arm.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: <71fa4302-2df6-4e55-a5a8-7609476c41d4@arm.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: 5B6C12001A X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: jye9mwx3qmfyfoqb3tm6znceqhujif7r X-HE-Tag: 1708955431-103018 X-HE-Meta: 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 u5oex1CB trG9m4gkKgrLnVaa+eZxPzs74JyS0uAJSJpK9xmTgYFB6ILmN4F43pKGLnSGgaludMGd3wNQgkeQoZdszxGrdg0tgbcvn5trhQxkslF1lQ6xz23Ng7TUYSmSzeg0EMR4rL198v96IoGAwMf2uFbqmkeXlngnC9XvZRZ9Mgvu2tmaKkne9eMyzJmxW7vqwts2OP+7Ulh5uDbxACdCF/FRqYYdjSBqZ33bd7lnk8ZsRIVOmT9C0ao1x+9h/U+W72AFf3NqnXJt6hLkBH12i9JvbYDqbfu1e5JVUTBKG 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 26.02.24 14:46, Ryan Roberts wrote: > On 21/02/2024 08:50, Barry Song wrote: >> From: Barry Song >> >> The purpose is stopping splitting large folios whose mapcount are 2 or >> above. Folios whose estimated_shares = 0 should be still perfect and >> even better candidates than estimated_shares = 1. >> >> Consider a pte-mapped large folio with 16 subpages, if we unmap 1-15, >> the current code will split folios and reclaim them while madvise goes >> on this folio; but if we unmap subpage 0, we will keep this folio and >> break. This is weird. >> >> For pmd-mapped large folios, we can still use "= 1" as the condition >> as anyway we have the entire map for it. So this patch doesn't change >> the condition for pmd-mapped large folios. >> This also explains why we had been using "= 1" for both pmd-mapped and >> pte-mapped large folios before commit 07e8c82b5eff ("madvise: convert >> madvise_cold_or_pageout_pte_range() to use folios"), because in the >> past, we used the mapcount of the specific subpage, since the subpage >> had pte present, its mapcount wouldn't be 0. >> >> The problem can be quite easily reproduced by writing a small program, >> unmapping the first subpage of a pte-mapped large folio vs. unmapping >> anyone other than the first subpage. >> >> Fixes: 2f406263e3e9 ("madvise:madvise_cold_or_pageout_pte_range(): don't use mapcount() against large folio for sharing check") >> Cc: Yin Fengwei >> Cc: Yu Zhao >> Cc: Ryan Roberts >> Cc: David Hildenbrand >> Cc: Kefeng Wang >> Cc: Matthew Wilcox >> Cc: Minchan Kim >> Cc: Vishal Moola (Oracle) >> Cc: Yang Shi >> Signed-off-by: Barry Song >> --- >> mm/madvise.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/madvise.c b/mm/madvise.c >> index cfa5e7288261..abde3edb04f0 100644 >> --- a/mm/madvise.c >> +++ b/mm/madvise.c >> @@ -453,7 +453,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, >> if (folio_test_large(folio)) { >> int err; >> >> - if (folio_estimated_sharers(folio) != 1) >> + if (folio_estimated_sharers(folio) > 1) >> break; >> if (pageout_anon_only_filter && !folio_test_anon(folio)) >> break; > > I wonder if we should change all the instances: > > folio_estimated_sharers() != 1 -> folio_estimated_sharers() > 1 > folio_estimated_sharers() == 1 -> folio_estimated_sharers() <= 1 I'll send out something that wraps that in folio_mapped_shared() later today or tomorrow. -- Cheers, David / dhildenb