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[2003:cb:c719:7700:ef08:112b:278d:7d90]) by smtp.gmail.com with ESMTPSA id n41-20020a05600c502900b00413fe69037dsm2850831wmr.44.2024.03.15.04.12.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 Mar 2024 04:12:39 -0700 (PDT) Message-ID: Date: Fri, 15 Mar 2024 12:12:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 5/6] mm: vmscan: Avoid split during shrink_folio_list() To: Ryan Roberts Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yin Fengwei , Andrew Morton , Matthew Wilcox , Huang Ying , Gao Xiang , Yu Zhao , Yang Shi , Michal Hocko , Kefeng Wang , Barry Song <21cnbao@gmail.com>, Chris Li References: <20240311150058.1122862-1-ryan.roberts@arm.com> <20240311150058.1122862-6-ryan.roberts@arm.com> <1db242d3-5ff1-4ef5-b20a-578a317fa859@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: <1db242d3-5ff1-4ef5-b20a-578a317fa859@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: 8bit X-Rspamd-Queue-Id: A71364000B X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: j8xjow14do5prpm17fktnxnkwe4s5zqk X-HE-Tag: 1710501163-438939 X-HE-Meta: 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 0jkG+NfJ jxGKE4acnrhCzdEZF/4vNgxZkDNXG/yPj4QI8+GOE4TF4UkEvdx4kqmJyle23n+LQ+Nz0Y7PWp1rTgGYJ1nwtr0I6bdqbR6rdvev1BasgTQxwQezjlUlk0HVaD44g4n18sVIdEAuaWFIQNclKTPYOcvE7x8vqx/fMbm1Us8+XsHfyAVH9DgE+XVMWTpWmesyfrPctNlz0penpCq4zirN8M/kY2w== 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 15.03.24 11:49, Ryan Roberts wrote: > On 15/03/2024 10:43, David Hildenbrand wrote: >> On 11.03.24 16:00, Ryan Roberts wrote: >>> Now that swap supports storing all mTHP sizes, avoid splitting large >>> folios before swap-out. This benefits performance of the swap-out path >>> by eliding split_folio_to_list(), which is expensive, and also sets us >>> up for swapping in large folios in a future series. >>> >>> If the folio is partially mapped, we continue to split it since we want >>> to avoid the extra IO overhead and storage of writing out pages >>> uneccessarily. >>> >>> Signed-off-by: Ryan Roberts >>> --- >>>   mm/vmscan.c | 9 +++++---- >>>   1 file changed, 5 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index cf7d4cf47f1a..0ebec99e04c6 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -1222,11 +1222,12 @@ static unsigned int shrink_folio_list(struct list_head >>> *folio_list, >>>                       if (!can_split_folio(folio, NULL)) >>>                           goto activate_locked; >>>                       /* >>> -                     * Split folios without a PMD map right >>> -                     * away. Chances are some or all of the >>> -                     * tail pages can be freed without IO. >>> +                     * Split partially mapped folios map >>> +                     * right away. Chances are some or all >>> +                     * of the tail pages can be freed >>> +                     * without IO. >>>                        */ >>> -                    if (!folio_entire_mapcount(folio) && >>> +                    if (!list_empty(&folio->_deferred_list) && >>>                           split_folio_to_list(folio, >>>                                   folio_list)) >>>                           goto activate_locked; >> >> Not sure if we might have to annotate that with data_race(). > > I asked that exact question to Matthew in another context bt didn't get a > response. There are examples of checking if the deferred list is empty with and > without data_race() in the code base. But list_empty() is implemented like this: > > static inline int list_empty(const struct list_head *head) > { > return READ_ONCE(head->next) == head; > } > > So I assumed the READ_ONCE() makes everything safe without a lock? Perhaps not > sufficient for KCSAN? Yeah, there is only one use of data_race with that list. It was added in f3ebdf042df4 ("THP: avoid lock when check whether THP is in deferred list"). Looks like that was added right in v1 of that change [1], so my best guess is that it is not actually required. If not required, likely we should just cleanup the single user. [1] https://lore.kernel.org/linux-mm/20230417075643.3287513-2-fengwei.yin@intel.com/ -- Cheers, David / dhildenb