From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1C3A0C5AC82 for ; Mon, 10 Aug 2026 09:22:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 053306B008C; Mon, 10 Aug 2026 05:22:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 004696B0092; Mon, 10 Aug 2026 05:22:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E353B6B0093; Mon, 10 Aug 2026 05:22:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 7F7196B008C for ; Mon, 10 Aug 2026 05:22:28 -0400 (EDT) Received: from smtpin10.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 1FD98406B6 for ; Mon, 10 Aug 2026 09:22:28 +0000 (UTC) X-FDA: 85084819176.10.09F57F2 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf02.hostedemail.com (Postfix) with ESMTP id 49AA88000C for ; Mon, 10 Aug 2026 09:22:26 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=gcoznZ5A; spf=pass (imf02.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786353746; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=6wQr3PYTUoSXpaDl5k0IG1zQOBI7tNXiUqLf3cd1RKg=; b=KCJ0itxi0XuN6aj06j9Hq1yiWkzg2gpFpLpSYLyZtwkkkU/bLumhbJW1T0C+sxwHQHNamd /sxA6KA/yeTi2hY/aoqGa6F89b1aDd16QxMgLcSyjeaZK9KpdpMc4AXjyMCn5ZrB4jqlYQ QS1T7Xwzc5Ib3KOpBqd1J6ehZP0Bdb4= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786353746; b=qRqC8WoxUL1RRuCE1HJXFwyqbLPb+Kl2TOKXftACxtdUF6OT6C88etx+Gb16Nw3MRZ8UvK zLpTDflaRpBcoyHMkkO7gojCtlOLt+C3hkjI4NWb+ef2mZvfkLmYyeGreDSNX5G6tUyeK/ ZiEsQ+6tbKT52bqfe7tI6a2DPbzaNjE= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=gcoznZ5A; spf=pass (imf02.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 67488434B6; Mon, 10 Aug 2026 09:22:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 459751F000E9; Mon, 10 Aug 2026 09:22:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786353745; bh=6wQr3PYTUoSXpaDl5k0IG1zQOBI7tNXiUqLf3cd1RKg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=gcoznZ5AtoqypeuzFMUFCV0SMZb31NgwLMyAOZz/m430M40GrLBfXae1BEO+LjcA4 XuKCG/K1eNaSIhwwyrXHHUUiAagMRg08hWANytGDAoToeNFKX4wR71XEYFGkFbUWjk xqs2uRpDOpUmvayAD1TsECcSybfbFE7IbwuCUQxc4kE3FZ6eF4eAJEg/qTFVk5suAe FstVMR84DcIukqC/PhHwIPZj3vMsyQyBIi/Yiy32UcvUROna5tfQH/+wkTGaeZLDOi d0eblAzJLiLUDuD98q1S66cpzfD+9zFh8IrH7rGPro3csMwEaReIYEyXaXQjHV5Z0Y tgGH+JPNFocaw== Message-ID: Date: Mon, 10 Aug 2026 11:22:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 14/41] mm/gup: factor out LRU cache draining for folio into lru_cache_drain_for_folio() To: ackerleytng@google.com, aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, tabba@google.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , tarunsahu@google.com, Vlastimil Babka Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev References: <20260807-gmem-inplace-conversion-v10-0-2fc18ee6d3ba@google.com> <20260807-gmem-inplace-conversion-v10-14-2fc18ee6d3ba@google.com> 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: <20260807-gmem-inplace-conversion-v10-14-2fc18ee6d3ba@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 49AA88000C X-Stat-Signature: e3tbwn7kuq5prr3doee1xteonpo8wf1i X-HE-Tag: 1786353746-732061 X-HE-Meta: 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 SLR80U80 YDkUpZXWsYfvRrRbEuTF2/0kb0gXQWCr84LifzgLnilZBzNgCdytBDNehJEA4ey3MrNeDlOTYEx2zGUJu9rsz+cFYhM4zyV+24VVEiBAodMeGTJIqgBgRZU2MpkmZMdyKYWlbJrgSNSyb+EmbvHACZAwBMRt/NZMPLs2INr+63svUW/Oijo6xMwZ4jW0+PCvW5jKi1Z7Wop2BGMUdhIo3W7m6J3wurxEUF+xceiJ+zf7ZFJGjd+Fz5I3u1eSM2SBX50HsrwwZrRLSl5+D00ww6/G3Uwfzp8Fg0C6rArkDXQx37dXcBX8DXFyXBbaBwidN4TqW5mtjLUqMNJOiFv1nfuACkmwfYOnRZhcr Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/7/26 23:52, Ackerley Tng via B4 Relay wrote: > From: "David Hildenbrand (Arm)" > > KVM with guest_memfd wants to remove any folio references due to LRU > caches, as it really must only allow to convert folios from shared to > private when there are no unexpected folio references (e.g., from GUP > references). > > So, to drive the refcount down, it needs a way to flush the LRU caches. > Let's factor out what we have in lru_cache_drain_for_folio(). Document > it, and also mention that concurrent folio (un)mapping might, in theory, > miss detecting LRU cache references. Keep obtaining the expected refcount > twice to minimize the possibility. For the current and future user that > should work, and we don't really have a better alternative: we could > detect if the mapcount changed, but it would still be racy and add more > complexity with questionable benefit. > > Maybe there is a chance to avoid the draining entirely in the future, > by avoiding extra references from the LRU cache: Hugh thinks there might > be a way. But for the time being, this handling is unfortunately > required. > > Make folio_may_be_lru_cached() accept a const pointer so > lru_cache_drain_for_folio() can accept a const pointer as well. > > Signed-off-by: David Hildenbrand (Arm) > Signed-off-by: Ackerley Tng > --- If all goes well, this patch should go into 7.3-rc1. So once you rebase, you'd get it for free :) -- Cheers, David