From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 68525412276; Mon, 24 Aug 2026 14:13:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787580798; cv=none; b=GHBhVo3o5nDKcHiEEET+HJ4k8Da3Rrpf7SXeIAJQn0DykPfPzZo8tDQtsfyPgkoEHSsh8C6neUUBwZR7JhDcSL/pCWPAu1F0D0VKNG89TcY8p/oMZBVG5fyaKLiwVBbyh/eVqAPm42D8Gp35Qn1HO7NbbeWlKyA8dflPrPdPZRE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787580798; c=relaxed/simple; bh=5H0nEc59Q986HZLlpGguY+/gdQ4VjP7DPXfE8/3QAyQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IAYmEdBjYaEHeOX5D1ANvN/9yzRV6J502Tc7FuhLvNAm0hGfP1f5FoOWkTQVIP4paZcJSemOG7oy+f2LQSF+VN3EUOpWN1hoveAukDuW/P6KtZOotn8ns1eo8dUNf04zWQ3H9YxgL64tul/1cqk0cl0si+xQCaMiSm462OipKhA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dtElHEPw; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dtElHEPw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A325F1F000E9; Mon, 24 Aug 2026 14:12:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787580797; bh=UwPdrh+01Xqj47dnasafGAdC09bKCXp4sZUyzRQNWvc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=dtElHEPwNBnUAjSebU6MFkk5JZ7wdxDH0pEu5d85rPPv2hTujo2yfk9UH2/+wIjqv MjTyMq9G4xqDacg2PwrjhRfrpgSvPAVrvTLPSoTjD4e3MFiZ6KKWsUoDlwnlRvbvzf dQ8AECA2WmANRDlw6APiZmu5Lo8JRraWXZz55CqnDE6bKhO5zrB+OU68b7V1rfaOLr 2CyCTmXc4Dz7bwNos8WCzsX6/iElz8tZUBUWB9J+widR5o/CBGoZLI9IOm8CpTT7OR ZUk5UYSBeF2a9pXwVwIimwiupWnRbUcKZmhqo1P5zkLpkRrtaATyfoxZScTMsgfy+X rqC2jWaDhsoIA== Message-ID: <3d58eb3c-7a9d-4183-907b-46172664631c@kernel.org> Date: Mon, 24 Aug 2026 16:12:29 +0200 Precedence: bulk X-Mailing-List: linux-i2c@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v19 00/40] DEPT(DEPendency Tracker) To: NeilBrown Cc: Byungchul Park , linux-kernel@vger.kernel.org, max.byungchul.park@gmail.com, kernel_team@skhynix.com, torvalds@linux-foundation.org, damien.lemoal@opensource.wdc.com, linux-ide@vger.kernel.org, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, will@kernel.org, tglx@linutronix.de, rostedt@goodmis.org, joel@joelfernandes.org, sashal@kernel.org, daniel.vetter@ffwll.ch, duyuyang@gmail.com, johannes.berg@intel.com, tj@kernel.org, tytso@mit.edu, willy@infradead.org, 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dave.hansen@intel.com, geert@linux-m68k.org, ojeda@kernel.org, alex.gaynor@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, rust-for-linux@vger.kernel.org References: <20260706061928.66713-1-byungchul@sk.com> <359ea967-9b97-4584-88e6-bddb4044de2e@kernel.org> <20260821042143.GA40890@system.software.com> <825134a8-ceae-430c-b2fc-d1d0c7240f39@kernel.org> <178730572084.2852630.7732425311008244683@noble.neil.brown.name> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 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59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <178730572084.2852630.7732425311008244683@noble.neil.brown.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi! >>> >>> That's a good news for lockdep. (And even for DEPT :) >> >> He :) Where do you currently store the additional per-page information? > > lockdep doesn't need to store per-page information. Possibly DEPT > doesn't either. That would be even better. [...] > > maybe you put the folio which is locked on a queue or an lru or > whatever. For readahead, I think that queues / lru are not involved. We submit the I/O, and once the I/O is done, we unlock the folio from interrupt context. end_buffer_async_read() / iomap_finish_folio_read() end up calling folio_end_read(), where we do the magic folio_wake_bit(folio, PG_locked); It's interesting, that for writeback we never unlock the folio on the I/O path, but instead have the dedicated page flag to tell us when writeback is complete. > > There is no way to say "that queue owns this lock". Maybe that could > usefully be added - assuming coherent semantics can be designed. > > Somewhere else some other task takes responsibility for that folio and > the lock. maybe it dequeues a page, or maybe an lru callback gives the > locked page to some code. > That code then calls > lock_map_acquire_try(&the_lock_map) I'd assume that's what the unlock path would do from interrupt context. > > This says "this task is now holding this lock" (or more accurately "now > holding a lock of this class"). > Note the "_try" - that says that the task didn't have to wait for the > lock, it just got it for free, which in fact it did. > > Now if that task takes some other lock, lockdep will see a dependency > between the page lock and the new lock, and will accept or reject it as > you would expect. I guess on the interrupt path, we primarily unlock the folio lock only. But we might take some other spinlocks temporarily indeed, like iomap_finish_folio_read() does. > But I'd like to see a coherent > explanation of how the functionality offered by DEPT is clearly better. Yes, that's also what I am missing. Stating that lockdep is stable and should not be destabilized is not really a good argument. -- Cheers, David