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[2003:cb:c737:1f00:94ff:246b:30d0:686b]) by smtp.gmail.com with ESMTPSA id q2-20020a05600000c200b0033dedd63382sm9362042wrx.101.2024.03.18.03.05.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Mar 2024 03:05:17 -0700 (PDT) Message-ID: Date: Mon, 18 Mar 2024 11:05:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 5/6] mm: vmscan: Avoid split during shrink_folio_list() To: "Yin, Fengwei" , "Huang, Ying" , Ryan Roberts Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Matthew Wilcox , 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> <5cc147fa-492e-46c3-963d-2f6e6680dce9@arm.com> <878r2gwahg.fsf@yhuang6-desk2.ccr.corp.intel.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-Queue-Id: C6141A0011 X-Rspam-User: X-Stat-Signature: jjx6nhrui7ey1cc7guz3msw7rnpxkf9s X-Rspamd-Server: rspam01 X-HE-Tag: 1710756321-282652 X-HE-Meta: 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 zUSQ2oQy J8BXYY6WQh86JS0+ms+fhQeMEsmhJXERrJHKTpi4K9aFtaHziO3c9Zd3+PCfNAuuV4KqZoRnWuDYvxW/8h1ayMyv2CyHRZK83r82XSVBXSDdq7VhhEZ8DcdprpS7n+w+klIkmiAKzTXLs9utS9HkLQObk+9m3J3Mp6z5M 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 18.03.24 11:00, Yin, Fengwei wrote: > > > On 3/18/2024 10:16 AM, Huang, Ying wrote: >> Ryan Roberts writes: >> >>> Hi Yin Fengwei, >>> >>> On 15/03/2024 11:12, David Hildenbrand wrote: >>>> 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? > I don't think READ_ONCE() can replace the lock. > >>>> >>>> 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/ >>> >>> Do you have any recollection of why you added the data_race() markup? >> >> Per my understanding, this is used to mark that the code accesses >> folio->_deferred_list without lock intentionally, while >> folio->_deferred_list may be changed in parallel. IIUC, this is what >> data_race() is used for. Or, my understanding is wrong? > Yes. This is my understanding also. Why don't we have a data_race() in deferred_split_folio() then, before taking the lock? It's used a bit inconsistently here. -- Cheers, David / dhildenb