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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pUKIM-00CIgE-55; Tue, 21 Feb 2023 04:30:26 +0000 Date: Tue, 21 Feb 2023 04:30:26 +0000 From: Matthew Wilcox To: Hugh Dickins Cc: "Huang, Ying" , Andrew Morton , Jan Kara , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Zi Yan , Yang Shi , Baolin Wang , Oscar Salvador , Bharata B Rao , Alistair Popple , Xin Hao , Minchan Kim , Mike Kravetz , Hyeonggon Yoo <42.hyeyoo@gmail.com>, "Xu, Pengfei" , Christoph Hellwig , Stefan Roesch , Tejun Heo Subject: Re: [PATCH -v5 0/9] migrate_pages(): batch TLB flushing Message-ID: References: <20230213123444.155149-1-ying.huang@intel.com> <87a6c8c-c5c1-67dc-1e32-eb30831d6e3d@google.com> <874jrg7kke.fsf@yhuang6-desk2.ccr.corp.intel.com> <2ab4b33e-f570-a6ff-6315-7d5a4614a7bd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2ab4b33e-f570-a6ff-6315-7d5a4614a7bd@google.com> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: o5kfe1usnajzak99xch5rmp5ndn7381z X-Rspamd-Queue-Id: 6385F80004 X-HE-Tag: 1676953841-475917 X-HE-Meta: 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 jUqzO8no nnBlVuGiMlk825p6i5Kkl/N7mRl2+NnOzjk5yGJRV5D3uFUzv33szmsWi04ZQZsUCSmOzETbyvG7dxX6VpQhsQn6CqUrh6L4CU1Wi/Pqir5ffVCZ2Z75/MhggrBSRjcCjkkx/jyuhLXl6B8N/qe0Gew7OCPIQ57cbnKha7oXiKD/j5Fqoaz7rD2ya8a94mD4t03U/3MSbNJPozppgsgvrCpErlto57Mxk1lAC59g/1F/WIdujIW8f9yDix600yiz5e34L2yYZxRvGQ/nZtklntLkj1g== 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: On Mon, Feb 20, 2023 at 06:48:38PM -0800, Hugh Dickins wrote: > Yes, that's a good principle, that we should avoid to lock/wait > synchronously once we have locked one folio (hmm, above you say > "more than one": I think we mean the same thing, we're just > stating it differently, given how the code runs at present). I suspect the migrate page code is disobeying the locking ordering rules for multiple folios. if two folios belong to the same file, they must be locked by folio->index order, low to high. If two folios belong to different files, they must be ordered by folio->mapping, the mapping lowest in memory first. You can see this locking rule embedded in vfs_lock_two_folios() in fs/remap_range.c. I don't know what the locking rules are for two folios which are not file folios, or for two folios when one is anonymous and the other belongs to a file. Maybe it's the same; you can lock them ordered by ->mapping first, then by ->index. Or you can just trylock multiple folios and skip the ones that don't work.