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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7d3b8edbe29sm618288785a.91.2025.06.17.00.47.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 00:47:33 -0700 (PDT) Message-ID: <5bbf39b9-ddfc-4d97-8f08-8bd43223982f@redhat.com> Date: Tue, 17 Jun 2025 09:47:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [QUESTION] xas_reload() in iter_xarray_populate_pages() To: Dev Jain , ziy@nvidia.com, willy@infradead.org, dhowells@redhat.com, hughd@google.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, aneesh.kumar@kernel.org References: <20250526063524.22597-1-dev.jain@arm.com> <918d552a-085a-4529-8f20-a060b1f0c9f1@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: <918d552a-085a-4529-8f20-a060b1f0c9f1@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: N4dtCtBlzmFTpaR8uC85v474uEvvb7_TtoPUqXdsHZs_1750146455 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 20A0D100003 X-Stat-Signature: 3rx36ewsyiw7b9ad7a9qz9q3owwykx4r X-Rspam-User: X-HE-Tag: 1750146456-562638 X-HE-Meta: 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 81MOcvCh jZvMAq8F3l2BdKMZzHzukzHieOFoifjnvDHtazAlzJr8mYsFrAYRD9xG8579MbT8chen4329c71I5H8YVDUIAhwgEp9Xv/7Bua5Q8LRnOzdi/fQ6mMxPdrZlDXrH/B76c9yg6aGmGkd97JTQLm9LEFQfy70TFiC/ktvufeDHrlMVP9jGx1ESy8H73bopf1vSqIr22CyEYMn7bS3Q65ifD4XMJYJy+9PaR7v/h7CYT5mEyjAOTo6Ha58/FvzvdA2qosW4pIwht4+8BHq0ukwSx/9D41LbhCJtfTe+qE49wuCpPFIJ2TIeI1juBapbV6JMRuOwULgi8kqVp+iG0n7HZmsF7D1627i7iGJNo9MJ4Q3QJBHqI5RDj8sYITz41byLzrZ8AFJrv2yQyt5krOMW4RiT4Xa+mduqKhZ3uopQV5WlCp7EvfCQRYwLSPhY1O1LeM5pS 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 17.06.25 07:10, Dev Jain wrote: > > On 26/05/25 12:05 pm, Dev Jain wrote: >> Hello all, >> >> After doing an xas_load() and xas_retry(), we take neither a reference nor a lock >> on the folio, and we do an xas_reload(). Is this just to reduce the time window >> for a race? >> >> If the above is true, then, there is a negligible window between xas_load() and >> xas_reload(), because only xas_retry() exists between them, so why to even reload()? >> >> Thanks, >> Dev > > I do not completely remember our discussion in THP Cabal; I recall David Howells maybe > saying that the folios are already locked, so it is safe to do xas_load and then do > a folio_get()? Even if we remove the redundant xas_reload(), I still don't understand > why we won't need xas_reload() at least after folio_get()? I think the points where (a) this should go all away soon (b) there is the expectation that the folios cannot get truncated concurrently. So we can do an unconditional folio_get(), don't have to check folio->mapping etc. (c) The xas_reload() seems unnecessary and can be dropped. -- Cheers, David / dhildenb