From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794256609; b=qjdcIlMAwEYjeWUWFntJcNYufovtMAIZq8sQXwdYCmiLbpE8xh8fwfwPCZwn5HJFT1Qe YVw6/X58rnNtM28jUDer01qSsL0LcDKldhNWKJVXsNpcPeAxknbXznnaLSppaThW79c69 pZCYp3TFDzeBKiwX+eXEm6tKf4uSe1eReVZJCWptIWsRbpxCyWBDb+LgvVzG61Ay2U+De HsQcC/lB1lpOlPrUZIsIvlzCIWrY23XPbKDqLKFjL/8K77QERFVX9AkoHOyvbYoGiv2AT aW7zGsM+YnqDRqIE26WU+Kxr6GaHt1beg5N0+ZhXCJcPHJI+ybqHqiB3mz3z4/X8WxA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794256609; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=9oF9audfKANIUeCSjRE2UxoYSJ8eZS3TN4Enjb9NBvA=; b=UuSg9/ourQ8roYT9l7UEWs91TH0GzJZAz4E6qCxs78xav5BPJ2zRggTGC9MStXx91GHI xzxVQspZioxJSG3ja07NE4IZrySWidC4Z/TWwYQZZBYMq5T4oGSX/08eVoojcVD5A4z5W keuI/KYCGB1gGs+/1VvRsXDkpiy62oVpffZwCjm2D205GGUHnZKbt7ZaNmyJWOTdHNFl9 7JqTyToFWFbXpfa7WhNQv/dxSfmYyPzLWt8wv9xRieRrgKBOkdvakGxzloVy7D0ISu2ik 3iwxMaBN/HM81ua+YJXbgs1meT8K8lPFKsiq9WUsHQv62S8wumOZNdCUhm6Q4omReNg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=EefOnyi2; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BF515606A337 for ; Mon, 9 Nov 2026 20:36:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=EefOnyi2 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 459541F0089F; Mon, 9 Nov 2026 20:36:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794256608; bh=9oF9audfKANIUeCSjRE2UxoYSJ8eZS3TN4Enjb9NBvA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EefOnyi2juZx4CLNe0tV/hc9vymdy866x18Xt0oh0y/RHhUiC1T/CW9gCl5MSPyyt bf9WQ0uqfn2sToC15cCy7r5Bpgb7yZAhbXviQsZDSb8Snt77HjRuBbGMQ51iw4pC56 oBPeCrcM2GaD75nLGNISe9o9KeKQ/Ysd4A3crHHnGBXct/ilMTser/ljPM67RbVuO5 GwWwD1mG0kaH2gncGE4ZZo80n8bW3zDa95/z85GZkgJqJExJlZssZjcxtQLmefRWTA 2HtvvweWAAE5dQ9cqHshfsygxx8LjajMIFFzEQYTVLhmOuDgPmQqvQKtSQdJIQahuy mBAA7yyrGQMYg== Message-ID: <3a137aa0-d0b5-4267-b64c-d58ab4235603@kernel.org> Date: Mon, 9 Nov 2026 21:36:40 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/migrate: don't batch the TLB flush when there is nothing to batch To: Zhiteng Qiu Cc: Andrew Morton , Ying Huang , Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Alistair Popple , Xin Hao , Dave Hansen , Yuan Zhong , Shifei Ge , Jianyong Wu , Shijie Huang , Yibin Liu , Fengyu Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261106041628.1177963-1-qiuzhiteng@hygon.cn> <20261107143456.1590658-1-qiuzhiteng@hygon.cn> <20261109122915.2150586-1-qiuzhiteng@hygon.cn> <20261110001816.2186986-1-qiuzhiteng@hygon.cn> 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 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 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: <20261110001816.2186986-1-qiuzhiteng@hygon.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/9/26 17:18, Zhiteng Qiu wrote: > On 11/9/26 14:07, David Hildenbrand (Arm) wrote: >> For the future, please don't send new revisions in reply to old revisions. > > Sorry about that. I'll send the next revision as a new thread. > >> Is there no way to avoid that boolean? > > [...] > >> This is all information the caller could provide, and the caller could just >> provide the TTU flag then instead of passing a new "bool". >> >> Also, likely this check can be put into a separate helper function. > > Agreed. I'll move the decision into a helper called from > migrate_pages_batch() and pass the resulting flags to > migrate_folio_unmap(). > >> I am not quite happy about the folio_mapcount() check, though: as soon as we >> optimize try_to_unmap() to batch better for large folios, it would be just plain >> wrong. > > That makes sense. A large folio's mapcount alone would not tell us > how many separate flushes are needed once its PTEs can be handled > in a batch. > > Would it make sense to restrict the optimization to a single, > singly mapped small folio and keep batching for all large folios, > as in the scope of v2? The changelog performance numbers were > measured with the v2 check. Or do you have a different direction > in mind? Likely best to focus on small folios first. -- Cheers, David