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t=1784119244; bh=i70MI3s/daHgb9WcIfx/WVMuhZ4GwOjC+i/kHkbzay8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=R/+DW4QsHagJtrTm/PTF1fKFkQUwn2RCbCtKWbYz32A5aQmLRXgW0gznkbmzP//tx 8wh8fGPqa+d90N7VKYCtVtrpkSTggPM4uj8Hg8EPVH9x+mjALJBzvrazvWN2J5MX1l epqL0VPTJr6z6ia/yLeoW/JNUQ8zmIjRDW6gxICJvzVJeqtgOUkQw1SJ/gkEJIM/Rr wbwFkdjJZaQ8qS1eF8FKkxSvz1nYKrbKum038JZNG412M/6b88ltOpD2mHwv2c5MB2 k+ZOISYGwdB0CUMoaOYAoHnCIe6nwYqOmRjegD1qW3p3xpnswgQPW/raFCWgAfFIfF /aXPl5Id2ry3A== Message-ID: <8f7f0a6f-d819-4a56-bb5c-d690664dd80e@kernel.org> Date: Wed, 15 Jul 2026 14:40:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: avoid overflowing migrate_vma collection arrays To: Zi Yan , Alistair Popple , Balbir Singh Cc: Matthew Brost , Andrew Morton , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Kefeng Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko References: <89d20411-4915-43e8-9808-3a7fbd98d2ab@kernel.org> <57cc487b-6ec3-4ca6-8735-f37644e2b0ab@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 7DE9614000E X-Stat-Signature: 1dpqdsc5khudek55rr4wdtx4fr7jfxb6 X-HE-Tag: 1784119246-823910 X-HE-Meta: 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 VrGKhPZ7 nKwYhZYHC323EWT4yyKwQVW+RdxKbvmp7gBdeCABBUx1jbi7G5ECYiamF+4Gh9c8LO77JTEEN292G/MjZrjGMp40oydju0DKaZbdWaMr/m7/Rc7jtHnQcdk/5dGl7VL5rZoN7tPvOTbH8/o1Wv0PJ3MFuqumDWgywGhyP5lSHHVeX5DFex8bQ25wKoqNRxXf6P8O8f20HE/FRQLDq4i6unsoY8h8O010FtVloU7aPWd09jgZhW5FDbZqt8GrOWA4O1akQ1Uziq9mGLORt4gHDXXT0WPDsXhqzOeDLRMDbdvol1DNOZTlSxVZwr5KAixPwzohWe6OvD5Ht5h8PsRy0Wdc2bXbBWZC6g7l6X+k3eRED7L739mkA2hp/iCI6UC6bR4JStcyl64+Wzsn1W4KVt1lyyg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/15/26 02:59, Zi Yan wrote: > On Tue Jul 14, 2026 at 1:30 AM EDT, Alistair Popple wrote: >> On 2026-07-14 at 10:10 +1000, Balbir Singh wrote... >>> >>> I had a patch to add tracepoints to the code and some of that instrumentation >>> included this data. A combination of the trace points + hmm_tests will help us >>> get some data to start with. >> >> But hmm-test already has a nice bandwidth benchmark :) We just need to force >> the slow path. That used to be easier before I simplified the trylock handling >> but with the below patch applied I get quite a lot better perf from the >> optimisation. Note the patch isn't entirely correct as it assumes any locked >> page was locked by migrate_vma_collect_pmd but it's good enough for the purposes >> here. > > Thanks for the numbers. If I read them correctly, the optimization > has about 3x throughput of unoptimzied version. The optimization has to > stay. > > I will try to come up with a fix that resets collected PFNs, reverts > established migration entry along with putting folio ref, and restarts > from the beginning. IIUC, with the page table gone there are no entries to revert. We only have to take care of folio lock+ref. Which raises a question: how can the page table be gone when it contained migration entries? Probably MADV_DONTNEED could clear them, followed by reclaiming the page table, maybe. -- Cheers, David