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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38058b47946sm9154961f8f.47.2024.10.28.03.43.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 28 Oct 2024 03:43:33 -0700 (PDT) Message-ID: <154430c4-7b17-443f-8628-ef3bb7738ae9@redhat.com> Date: Mon, 28 Oct 2024 11:43:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH hotfix v2 2/2] mm/thp: fix deferred split unqueue naming and locking To: Hugh Dickins , Andrew Morton Cc: Usama Arif , Yang Shi , Wei Yang , "Kirill A. Shutemov" , Matthew Wilcox , Johannes Weiner , Baolin Wang , Barry Song , Kefeng Wang , Ryan Roberts , Nhat Pham , Zi Yan , Chris Li , Shakeel Butt , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <81e34a8b-113a-0701-740e-2135c97eb1d7@google.com> <8dc111ae-f6db-2da7-b25c-7a20b1effe3b@google.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: <8dc111ae-f6db-2da7-b25c-7a20b1effe3b@google.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-Rspam-User: X-Stat-Signature: sd66mpjnyt8sz66hrnmw3id5dqibkhhd X-Rspamd-Queue-Id: A4816C0021 X-Rspamd-Server: rspam11 X-HE-Tag: 1730112188-163529 X-HE-Meta: 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 YmSiByms 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 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: Hi Hugh, mostly looks good to me, one comment: > +++ b/mm/memcontrol-v1.c > @@ -848,6 +848,8 @@ static int mem_cgroup_move_account(struct folio *folio, > css_get(&to->css); > css_put(&from->css); > > + /* Warning should never happen, so don't worry about refcount non-0 */ > + WARN_ON_ONCE(folio_unqueue_deferred_split(folio)); > folio->memcg_data = (unsigned long)to; > > __folio_memcg_unlock(from); > @@ -1217,7 +1219,9 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd, > enum mc_target_type target_type; > union mc_target target; > struct folio *folio; > + bool tried_split_before = false; > > +retry_pmd: > ptl = pmd_trans_huge_lock(pmd, vma); > if (ptl) { > if (mc.precharge < HPAGE_PMD_NR) { > @@ -1227,6 +1231,27 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd, > target_type = get_mctgt_type_thp(vma, addr, *pmd, &target); > if (target_type == MC_TARGET_PAGE) { > folio = target.folio; > + /* > + * Deferred split queue locking depends on memcg, > + * and unqueue is unsafe unless folio refcount is 0: > + * split or skip if on the queue? first try to split. > + */ > + if (!list_empty(&folio->_deferred_list)) { > + spin_unlock(ptl); > + if (!tried_split_before) > + split_folio(folio); > + folio_unlock(folio); > + folio_put(folio); > + if (tried_split_before) > + return 0; > + tried_split_before = true; > + goto retry_pmd; > + } > + /* > + * So long as that pmd lock is held, the folio cannot > + * be racily added to the _deferred_list, because > + * __folio_remove_rmap() will find !partially_mapped. > + */ Fortunately that code is getting ripped out. https://lkml.kernel.org/r/20241025012304.2473312-3-shakeel.butt@linux.dev So I wonder ... as a quick fix should we simply handle it like the code further down where we refuse PTE-mapped large folios completely? "ignore such a partial THP and keep it in original memcg" ... and simply skip this folio similarly? I mean, it's a corner case either way. -- Cheers, David / dhildenb