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imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=lZ9h4XlX; spf=pass (imf09.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776154289; a=rsa-sha256; cv=none; b=woHx36z1e1HKooDwpNgIXsWRBF+jWlZqS4CeEd97eIS8xbsSHvFXN1EFlf2c1jfHiCNwX2 2FQwq2dTVYVWvhVTqVb5mnqem3ROoOtEkAZ4o/VcuQOmSOlv4GkoOlByzsLnjkjj9DgO3W ej11EtwUH5AZTN5HjE1/7l7/Ws6ONBA= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 057D060018; Tue, 14 Apr 2026 08:11:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34A6AC19425; Tue, 14 Apr 2026 08:11:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776154288; bh=VxjOWkpHI39Iy08LBzZ4L8PQgORAVarz+9fIJCl1oO4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=lZ9h4XlX2/jn5beFHYWAGEYVf5VwdfmL5PcJOFc3kPDZwyqecdRki6/tfMTWTHIfz mQQ2Qe6HuoZE1dfg3E7FaokCCEuwWRCWqO8dKWmPjCblZqG1UC0h3AjUFCU5vpoDmv nLv7PRBGCqV4WJl8QBugDBNzUyANF8OVDBgQ0PFKkiV/sjz9q6XpZScJMVM0cwf1D1 kSRRhp2VZuND9B7zFxlFwnswNAllbwc8q9j4V5VExAa8UewkqTyCkA79I5xETjwKZq jpTAvWqysE6aviWnrDNAGuN5Ei0Umffr3aOb+10kAGiWM7dITwGmeiYVnvlhgqZdOW 48j3zFw92qrAg== Message-ID: Date: Tue, 14 Apr 2026 10:11:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/2] mm: make lazy MMU mode context-aware To: Alexander Gordeev Cc: Kevin Brodsky , Andrew Morton , Gerald Schaefer , Heiko Carstens , Christian Borntraeger , Vasily Gorbik , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <44dd86c0-1845-4dd9-b4b4-2cef6d1c6357@kernel.org> <665a19a0-47c2-404c-bd2b-482ab51b8f64@kernel.org> <896b3d93-8e60-42e2-b8bb-d3d4e8c99927-agordeev@linux.ibm.com> <534ed892-a6ab-454e-831b-e207930c35cc@kernel.org> <584f0f88-aef9-4a70-b0bb-abc797f741ed-agordeev@linux.ibm.com> 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-Stat-Signature: 97q6rtf9o6xasna97a1t68uibpnbsjqn X-Rspamd-Queue-Id: A342A140006 X-Rspamd-Server: rspam09 X-HE-Tag: 1776154289-993788 X-HE-Meta: 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 Kyvd5fd6 ypjUd/oWd5n9dnbzmoWeeN9L28ZVweU6Az2DIW6XVohRCFdEtRgwPM3lQvscPxGVvLMEbsQ/jKYtTJjMp56kPcdo+qcGH0i9ot+u1IGo7AgPMcyguXe1S+0VYVTcfYL2LywnA0kbQ9w2Rl2nHw+PExhNNW+WzT14R63DpMLbt2ZTDteDS2/BUQIhwSynOqsk3QQYFIQNlXlbOttTjSZQN3ou4fceFnpy1VokFW+frOPW5IBL96C/JQDRDpgB+ODWcmcTG Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/14/26 09:53, Alexander Gordeev wrote: > On Mon, Apr 13, 2026 at 08:32:11PM +0200, David Hildenbrand (Arm) wrote: >>> 1. copy_pte_range() operates on two ranges: source and destination. >>> Though lazy_mmu_mode_enable_for_pte_range() applies to the source one, >>> updates to the destination are still happen while in tha lazy mode. >>> (Although the lazy mode is not actually needed for the destination >>> unattached MM). >> >> So, here a >> >> "No ptes outside of this range in the provided @mm must be updated." >> >> could be used. >> >>> >>> 2. move_ptes() also operates on a source and destination ranges, but >>> unlike copy_pte_range() the destination range is also attached to the >>> currently active task. >> >> But not here. > > I did not quite understand these two comments ;), but I think > I address them further below. I'm saying that the second case is the problematic one ;) > >>> 3. Though theoretical, nesting sections with interleaving calls to >>> lazy_mmu_mode_enable() and lazy_mmu_mode_enable_for_pte_range() make >>> it difficult to define (let alone to implement) which range is currently >>> active, if any. >> >> Right. I assume you would specify the source here as well, or which one >> would it be in your case to speed it up? > > It is in all cases the source/old/existing one. Make sense. > >>> All of these goes away if we switch from for_pte_range() to fast_pte_range() >>> semantics: >> >> I don't quite like the "fast" in there. I think you can keep the old >> name, but clarifying that it is merely a hint, and only ptes that fall >> into the hint might observe a speedup. > > Okay, that simplify things. > >> Could performance benefit from multiple ranges? (like in mremap, for >> example)? > > No. > >> In that case, an explicit hint interface could be reconsidered. > > So all things considered, how does it look? > > /** > * lazy_mmu_mode_enable_for_pte_range() - Enable the lazy MMU mode with a speedup hint. > * @mm: Address space the ptes represent. > * @addr: Address of the first pte. > * @end: End address of the range. > * @ptep: Page table pointer for the first entry. > * > * Enters a new lazy MMU mode section; if the mode was not already enabled, > * enables it and calls arch_enter_lazy_mmu_mode_for_pte_range(). > * > * PTEs that fall within the specified range might observe update speedups. > * The PTE range must belong to the specified memory space and do not cross > * a page table boundary. > * > * There are no requirements on the order or range completeness of PTE > * updates for the specified range. > * > * Must be paired with a call to lazy_mmu_mode_disable(). > * > * Has no effect if called: > * - While paused - see lazy_mmu_mode_pause() > * - In interrupt context > */ LGTM! -- Cheers, David