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[70.30.145.63]) by smtp.gmail.com with ESMTPSA id bs15-20020a05620a470f00b006b61b2cb1d2sm32001007qkb.46.2023.01.23.07.19.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Jan 2023 07:19:05 -0800 (PST) Date: Mon, 23 Jan 2023 10:19:03 -0500 From: Peter Xu To: Mike Kravetz Cc: James Houghton , David Hildenbrand , Muchun Song , David Rientjes , Axel Rasmussen , Mina Almasry , Zach O'Keefe , Manish Mishra , Naoya Horiguchi , "Dr . David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 21/46] hugetlb: use struct hugetlb_pte for walk_hugetlb_range Message-ID: References: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 580742000D X-Stat-Signature: f5aex6bscia9b9d45os764aqc67mmprx X-Rspam-User: X-HE-Tag: 1674487148-37668 X-HE-Meta: U2FsdGVkX19wffh7wO82Od91oPdFroFUEOs3XDd7I+N7c4x7m67Yn9jabV/hbDvm3JnDAVyQtnOys33MV9ixuXqsXn+8KLBPXeLO7zTJo+Xtuyq6xhcdCp7IKIvJPskr1MYcVmSt/Oxg2pWjyOAKS46j4/TSvWn6UfCcpb9nfRAMoD4Kd0HaSh5PRwthjv0sS+ZITj91d2yDkM0b6UI+rvprLEXPj1op5SCH2DfJwPNGMTFZxlI4C5mx8eQKLHVQe1LouNg/0A6A6+xfuF73lkZTDBtSXgc169j1omHq+knkCp+/AQi3z3ezy3chwLBlJsOHoRGAAyMvq3U4zAWuK/9NvM0dnK9K4brCWPcRJHEotD2iIG8q5jhmLIUHNW0ej60VZZEAhA5sPWnETXJT/FSsd8hwj1JZJYDB5VCQAc7qPz0+JMXR6ck2tEkAE3DMBkA4o+q61bw2mFU3jcHNzrDdvqdobgRrJ0iuE76gtmVclV0H6NpLfM0Oo4PXca1HV5T8Etxs8YnxJTv2vwzv24OCQZ6DTzKP4HBguVhJDjSqciGf2vb2q9VfnfiPSid2HQQ1PpLYCpk7YraSR+bGftXDe0uMpNzUizciUhYUsq88twMKgVFa4P0NetOlZgirXXMocJpm2OpckUAlZCiGCvdLwrv6TN+s6wjxDaarD522FL39GnGDCycWihYyx60KJJJEGX5l/KRu7uvn4xcwnFpApCYEhKAYBw698LuUyqWJ/ZfCE07ERFekNQ2/P96CUEtx0Wt8YOuZUoaRcPkgt9pUj2vh9CyCkQwWIaPiNRF3zJPpTq8Q4tTbtByG2/bO/TRAP0zQyPDi03JsdCkUSLTWhhgy+jLFu8z+Sj4qraR+vnzPrAqXV+9UuWrM/a99gNdxuZz5bR97uvQ90fFQAlrJbcOyti9o99XJ0DcVbp2QCtF0ZH8kLH3bsiBCKxJOgX+Jm6I6iXzZBGxpwyw 6EyaFTqQ kKwAVyGq4NgUKHm7BlUZpu92tY3+aeQlo0tGCEnzZ1RFYI5vQJUjdUtjjhPK4LyzN+8mcK9uh1QMlabs22gVWPsBRvPe5kB+kVaqOLegSnufQDwCPlZdZAaHFUQWyS3NWWS29iNNWoww0bEr8eou68uoiWTRB/AUjlSQ5P5Fyg0TMKEtvVYbaFcQSJ7NwzjCUx5bWNMjwlHq9du6pASHf7clQBbWmlYeP7f9cDEcwCBXdARDQRRjVoHbwFR6MlzUc0/h4AlDfkzBQiGBj0iyzBxa2E4tGD/kzlXTw7thg/5wtkR9ewxCxjtzVHiz0UhzzsgftjCmp+9SUdo6EsWRaxKXwHFIxP8UE0g+pt6KDUhE/4pTFpYUsEuXE8HOG7YtaNeCv0AmTEjQfgqz72xPrcutTtcoDTXFsC7Ypy0OpoWXa2LI= 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: Hi, Mike, On Thu, Jan 19, 2023 at 03:44:25PM -0800, Mike Kravetz wrote: > On 01/19/23 18:07, Peter Xu wrote: > > > > Actually when revisiting the locks I'm getting a bit confused on whether > > the vma lock is needed if pmd sharing is anyway forbidden for HGM. I > > raised a question in the other patch of MADV_COLLAPSE, maybe they're > > related questions so we can keep it there. > > I can quickly answer that. Yes. The vma lock is also being used for > fault/truncation synchronization. Commit e700898fa075 make sure it is > even used on architectures that do not support PMD sharing. > > I had come up with a rather ugly method of using the fault mutex for > fault/truncation synchronization, but using the vma lock was more > elegant. Thanks for answering, I'll need to read some more on truncation later. Before that, since COLLAPSE will already require the i_mmap_rwsem write lock already, does it mean it is naturally race-free against truncation even without vma lock? -- Peter Xu