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 2D83DC982D8 for ; Fri, 18 Sep 2026 21:02:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C6A0A6B0093; Fri, 18 Sep 2026 17:02:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C199C6B0095; Fri, 18 Sep 2026 17:02:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B08D76B0098; Fri, 18 Sep 2026 17:02:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 6E4066B0093 for ; Fri, 18 Sep 2026 17:02:36 -0400 (EDT) Received: from smtpin09.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 324FA1C30A4 for ; Fri, 18 Sep 2026 21:02:35 +0000 (UTC) X-FDA: 85228106670.09.CF8E600 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf08.hostedemail.com (Postfix) with ESMTP id 573C7160004 for ; Fri, 18 Sep 2026 21:02:33 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="I/mV7mHb"; spf=pass (imf08.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=1789765353; 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=rT6GbagmOOTUela/pJbPVBxH2Xo3VSFNdj9hyDoNywA=; b=qVsWuGY3p4kfyDAnwLydp5H+b4fjjc2JbPkJfM0qVJPsao7No3JREVDtkT1x2MfUVMDFuS d8IGSsytI/gZC30+2qXeGivOWLcmSNqEtUm2T+L5JpTKEDtD+Vt6w8tuiF3w7/c/qesoDi w0CByCLeZpLnF3F40N74m7Em5egr4qk= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789765353; b=SQzlI4PvNy5ZItpX+csPbotTqR7WtAfTtemrC9Yk298A6rcZnuTDToBoBsaFlpI9FVj8h3 L/x5OubbErUu1m2pBSDFJ3bMX9+qNJzu2sKrbQSl054u6F1mGeAtMjeSCYK7k1zYYWCLcR rGi4WsDW28+ZtJD/dK1PR1l3PLZuqug= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="I/mV7mHb"; spf=pass (imf08.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 87C34409E9; Fri, 18 Sep 2026 21:02:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1DE211F00898; Fri, 18 Sep 2026 21:02:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789765352; bh=rT6GbagmOOTUela/pJbPVBxH2Xo3VSFNdj9hyDoNywA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=I/mV7mHbfio5LCWlsIrA3VXWdNmX6zkN0T5K014oTYvj006zO3GzpLIXJ7CbJUA28 YGQnYDEWeWsUNUDHGbYrpCHFqAOL6K9WO8od9M6vdofBGKlshgK9Fyk9U87ypOH3hX X1PJSRSsNWyftbusBP2eW9ZHRVfMSZCO2eAMvrcSQ5Y+Kp1dRmiHoV2op5NtccWp8D +2CyLiRi3SvZAgfYuGpTJaqj3FDviQpRSqZxVVd6poBv7C3ZbfQJ9B8KwseeoujDiA YnIiBhGed0ZjBazkYq/WEj6yWtsmKuinUwyeYpipgKNdciWrKR+fIodNVmm4rjpLOU 5qLs9TMSsCYkg== Message-ID: <4015259a-cc44-4bfd-b9c4-39ae96d48057@kernel.org> Date: Fri, 18 Sep 2026 23:02:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 12/17] mm/huge_memory: move anon_vma handling into the anon split helper To: kasong@tencent.com, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Usama Arif , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Chris Li , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Yeoreum Yun , "Kiryl Shutsemau (Meta)" , Shivam Kalra , Kairui Song References: <20260915-swap-thp-cleanup-v5-0-39878b37dfb0@tencent.com> <20260915-swap-thp-cleanup-v5-12-39878b37dfb0@tencent.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: <20260915-swap-thp-cleanup-v5-12-39878b37dfb0@tencent.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 573C7160004 X-Stat-Signature: 3ickotr3733c7mexzn7jrjkrpzmdjhup X-Rspam-User: X-HE-Tag: 1789765353-176498 X-HE-Meta: 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 iD/NqhSc 79owfVDBf8c+XM/Nfn7YSDaUiuN5Y2kchvTcspukwS5wQAzP1camjjnHRRGm463ULaCaGu3UvTMJyoLkXCUUSjoYlgAD5H5TC//VtHqzDBEtAif5HdUs+KKXJSiHYQcqvf4l4ewTomQIZTT/2NiPIv5g15exXbmaZ/E14m6KQgSgpY8MYm3lMMEeZkxj6Sj4L2J5SZT92Spa1KtHxsPwIR4ooaqXXLbZ4F0CCtj6Kn7NtbQiF1M17s3TI5Y0rMWU7o9YKO5JYRTljsRKxjG8VadsOe1F6fBRWAKLQfEdCpEObUkvovitXTAsELmockg8FeX8Y7MkTw0mzPrpZjLNA5vRvSp9IYsNmUdJ0HYkd1eUa6DKMIJHgM8h4a31giS7QXI5T Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/14/26 19:14, Kairui Song via B4 Relay wrote: > From: Kairui Song > > Only anon split needs the anon_vma, and it only needs it to unmap and > remap. Move the folio_get_anon_vma()/anon_vma_lock_write() pair out of > __folio_split() into the anon helper next to the folio_mapped() > check that already gates unmap_folio(). > > This makes the anon_vma conditional on folio_mapped(), which is a > behaviour change but should be fine. folio_get_anon_vma() returns > NULL whenever !folio_mapped(), so an anon folio with > folio_mapcount() == 0 used to get -EBUSY from split_huge_page() and is > now split instead. A realistic case is a THP that has been fully > swapped out and is still in the swap cache: swap PTEs do not contribute > mapcount, so it is !folio_mapped() but still alive. > > That should be safe and right to have because: > > - folio_ref_freeze() below still rejects a folio that picked up any > reference, a mapping or a GUP pin, in the meantime. > > - A parallel split is excluded by the folio lock. The anon_vma > write lock was added to serialize split in commit 062f1af2170a > ("mm: thp: acquire the anon_vma rwsem for write during split"), when > split_huge_page() did not hold the folio lock throughout. commit > e9b61f19858a ("thp: reintroduce split_huge_page()") later made the > folio lock a caller requirement and added the folio_ref_freeze() > scheme, so that has been covered ever since. > > - Unmapped path is already exercised by folio_split_unmapped(), > and the swap cache split already runs well for a partially > swapped-out mapped THP. > > - A !folio_mapped() folio cannot become mapped meanwhile: mapping it > requires the folio lock. > > For mapped folios the anon_vma write lock is now released before > __folio_split() unlocks the after-split sub-folios, where previously it > was held across that loop; that window is harmless as the sub-folios > stay folio-locked and referenced until it. > > Reviewed-by: Zi Yan > Signed-off-by: Kairui Song > --- > mm/huge_memory.c | 58 ++++++++++++++++++++++++++++++-------------------------- > 1 file changed, 31 insertions(+), 27 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 8fc1dd5b8354..a4c2e38f4a6d 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -4029,16 +4029,38 @@ static int __folio_freeze_split_anon(struct folio *folio, > struct swap_cluster_info *ci = NULL; > int old_order = folio_order(folio); > struct folio *new_folio, *next; > + struct anon_vma *anon_vma = NULL; > enum ttu_flags ttu_flags = 0; > struct lruvec *lruvec; > - bool need_remap = false; > int ret = 0; > > + /* > + * Unmap/remap needs the anon_vma, so we first take a reference on > + * it to prevent it from disappearing, and lock it for write here, > + * letting unmap_folio() walk the rmap with TTU_RMAP_LOCKED. > + * > + * folio_mapped() is not stable here, but it can only change in > + * one direction while the folio is locked. The mapcount can drop > + * to zero at any time, zap_pte_range() takes no folio lock. It > + * cannot go up: swapin, migration and uffd move all lock the folio > + * before mapping it, and fork only copies PTEs that already exist. > + * > + * So if we see the folio mapped, the worst case is an empty rmap > + * walk. If we see it unmapped, it stays unmapped and needs neither > + * the reference nor the lock. Anything else needs a reference > + * first and folio_ref_freeze() below catches it. > + * > + * Note a swapped-out THP counts as unmapped here as swap PTEs do > + * not contribute mapcount, and they are splittable. Helpful, thanks. I'd rewrite the last part to "Note that entirely swapped-out THPs are unmapped but can be split." Acked-by: David Hildenbrand (Arm) -- Cheers, David