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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776105138; bh=EvxSafiBWABrGah99HN0FwITRI/21BtvzrpeZ2gtImA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=IVNfHTbBPdeNKO6fGf9PMgz2JYDGmEN40iDFS9drIkBgKY/BjyJU8cx3jqAgXJi1s phtWvNieJ6dW5qnOZgFUFFr8cgCA1BwCpd5Q54iUf/H60Nftae+WbZzb52hmRwblG5 z44DNFBsSSzxraEOk/qn7aPM4gBm/+e5Q4DrlrBzzt8qwN/RVWuQSG+ABIRafe6Rcm Wpj5R3ZFqXgTWhUsFNP56EMv06Jhbu6LETT4xFDyomkTzRswQK3kLiwKq52Ru8bfhN Ry+6mMtYAjkMC+yfBfr7r7KsmLfKbfG9v4S81QebzTH0IEL9k/WzpZbWf0vTb+V9a7 1gU3BIO3J0ADQ== Message-ID: <534ed892-a6ab-454e-831b-e207930c35cc@kernel.org> Date: Mon, 13 Apr 2026 20:32:11 +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> 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-Rspamd-Queue-Id: 01008180007 X-Stat-Signature: 6a7ffzmgb6cfdbbw43c38ihkt4et1wss X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1776105139-882729 X-HE-Meta: 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 K2hzuzFE WNhd6R5d8RJAgpyPWcMMJkioUnVODB+GVY21+bn7NSA7dlwtrA08YvuJeAF+oY2lselYxFKz+OyYV2EZXaqyC49cxLNANdEMOuu2yVNboA1im/xqMCK/lzVqI7gQRa7Yo1/mXgRwh7sYQf6ujSG4YvXh3SaJH8G4RB8Zr+sbldBuI0PAkRZxApBOXn70/MXnKWyZ94xaOhF4PQPZ6J+UoNseRnCjwBCx09vwPFePjZUKKPGAMCC0el6q5I+hjUSJFpEQ2 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/13/26 15:43, Alexander Gordeev wrote: > On Tue, Mar 31, 2026 at 11:11:22PM +0200, David Hildenbrand (Arm) wrote: >>> >>> The only implication is "only this address/PTE range could be updated >>> and that range may span one page table at most". >> >> Probably phrase it stronger. "No ptes outside of this range must be >> updated" etc. > > That turns out to be bit more complicated. The below cases do not fit > such a strong requirement: > > 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. > > 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? > > 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. Could performance benefit from multiple ranges? (like in mremap, for example)? In that case, an explicit hint interface could be reconsidered. -- Cheers, David