From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C07D93CF209 for ; Fri, 18 Sep 2026 20:53:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789764835; cv=none; b=FAgEtS+nlx1E34VK4s4DlJInE2WsDKtjcsIeddrfSAoXfCTlNiFI0+fqtl9LuBGs2UMDfbH3bLkPif4+01g0hyY+HTGvIoZ+SUuO81+DZlEvWxRDzvlsvuLd+eR5an8sWvy3dNW0QS4HsJ9kUXomiCjylb0O8zkTmcim2pFVp5c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789764835; c=relaxed/simple; bh=Qqhh0Cu8gO4U0oF10cUD2923SVElRu0xgwRbO2RJhZE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qbDcL1LaH+lLvGEtSYuQ1vr1voLqvTdx1BSFTZKNmc4vlVgn4gD1xMISX1W64EYU1LJOo5wMjI+2CJAPJuYuD/V1etvlepKtUcyAM7IHUN6eFjRG3oPHQhFE1h5L9kmQFFvMboe+QmNg8rRfCMA7hFQwPiStFuJG6HjgCN80Ni0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Kn6cunyI; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Kn6cunyI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29BD21F000FF; Fri, 18 Sep 2026 20:53:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789764834; bh=xubuskVOjl35A2T8LbXWyaJic0HJ1gjUagG1E7uyg5k=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Kn6cunyIes7b/fgeRfTD/r8Fz5Dt/p48ZFG59t5T2b5RHLeaNgCTrqw7SoEvlPOI5 OvuHjFp9mBWp2eSxzlYCzHbBrSV8vl/DXuPzPJZsbYv0Xuqx3JThxg5gE7p21r47NM re8B0ycP+LBJEhifDZxmaPWvMaTdbkP9L8TH7qLJTIaTctBBzxc/RuD/7RF6jFkHb8 KWnVoWNdO0FqVgOZmWwuAtlvnO4A/sZK0V15/LeRJeHFJOPaq8+/KJ7WwXC3Fux/3b Sy/yzfOLjEbN8O91kS4uuktMUrONkl0khiUu0A6+wRjAt+8vW3dCgUQdRS96CC41GY RUB7RSuRPKQLg== Message-ID: <475ff6df-c8ef-4681-be83-2fbd7a68c417@kernel.org> Date: Fri, 18 Sep 2026 22:53:45 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 10/17] mm/huge_memory: move the racy refcount check into unmap_folio() 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-v5-10-39878b37dfb0@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-v5-10-39878b37dfb0@tencent.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/14/26 19:14, Kairui Song via B4 Relay wrote: > From: Kairui Song > > The check only exists to avoid the expensive PMD-splitting unmap of a > folio that cannot be split anyway. Move it from __folio_split() into and folio_split_unmapped() > unmap_folio(), right before the PMD split, so both the anon and file > split helpers get the early check without repeating it. > > unmap_folio() now returns -EAGAIN if the check fails and the split > helpers propagate the error. folio_split_unmapped() drops its own > copy of the check: it works on already unmapped folios and the > definitive folio_ref_freeze() in __folio_freeze_split_anon() still > catches unexpected references. > > Reviewed-by: Zi Yan > Reviewed-by: Kiryl Shutsemau (Meta) > Signed-off-by: Kairui Song > --- > mm/huge_memory.c | 29 +++++++++++++---------------- > 1 file changed, 13 insertions(+), 16 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 77bf68c9b9af..859aefda7356 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3539,13 +3539,17 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, > split_huge_pmd_if_needed(next, end); > } > > -static void unmap_folio(struct folio *folio) > +static int unmap_folio(struct folio *folio) The semantics are special: a return value of 0 does not mean that unmapping succeeded. It might have still failed, but remap_anon_folio() must be called afterwards (for anon folios). Might be worth a quick comment. In general, LGTM. Acked-by: David Hildenbrand (Arm) -- Cheers, David