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=1793609012; b=AMfIyQn8cuSvB+uq/tYg/FTnwuW8FEZBoxacUaJ2wh0b8qLQhvWNdg8O0cQa0bJGaVbf 5x6ylIT47P+gpJQb6yV9/fw8ai8Gl9sJ/tdlkzQCB2ridh8io+QRDgFhm5Zy/D1W/5d0/ N+fmUL09U+UKBs+XATvXGB3HpUVJpmBZgR6MBbKNr+P5KQBNYA/gsk5LU60GEAoNTfzB3 IpelJPEG3iclJJJIhFysMKPDgb6pcX59drQyQGzfY2vVu9Ro+Blyo4Z0aX1Q3Qsr6ELq5 l8XLJiNw3CBMt+vXOJRJFovOSfs9GM5sbV0kBNMYK+49XjFXovi86W1nwWVU75ip2Jw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793609012; 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=H8IZTJpEEUQHCCQekZ6Kkx0jDr5Kasg15y/uILRyENE=; b=o7YSMfunxyEAbxKFey74rRAEazj5NSY0GxZt9ZtrkwKI38mmZ+As34Ka0LSJS8WXz92T BYF3eVK6wK4IFOw9aoqah5Dg/lGyaGUTc0dgzQ3TFpYW0HcvJjl7LfF3/iaPSAiQP2ICU TFgM9QRQ9/CcwgrRX9/3LxX4XOwjxKdAJfpEpPEYme78lfecK4vcApSc66SJqgJKsD+/H 6iYoyWKm8x5cbxOj0VoxQ6BFL20u43GUTgiNYXOD5kuHn0czieEYVxtQZVAiPAtmlO/Y/ U5Y8PLm+gwSxcCXnh9Muh8bk2WlxiGNHim0xXozqcCpCFgwkl/2zF0SwR15laOb2Zwg== 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="XT9e/Ixt"; 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 2B9F8606A324; Mon, 2 Nov 2026 08:43:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=XT9e/Ixt Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6828E1F000C1; Mon, 2 Nov 2026 08:43:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793609011; bh=H8IZTJpEEUQHCCQekZ6Kkx0jDr5Kasg15y/uILRyENE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=XT9e/Ixt2VRKUBN23d6OsOv+YMnoKfPXyhSCtL4boUac9vLUICBrJ0K9uMfnzwn8o 8w6CaciZpkg7HYzLmGTDy0GmvXtDftudG9AZsZ8fpFkWcM+2wEdatcb84CTCGUfnpZ cs+D/UPYJNOIXMDIP+HKhmaFQg4BmBYB3IwVszRH6lTKMRGoAlAougpHDlVDG4aJgj oI/bJZ7obLwyLwTT4H5TkQ0hyaQyAYbKcqCk+bfUpq4OlUR1Ku2FM5csVvyStFzPrG T3vuoQwcx6zUl7zjks4G2gn+tvaoLeTq7lqf92onTtvFLzQraAtlRksghdQAkDXXyY PPcnf7RdagpLQ== Message-ID: Date: Mon, 2 Nov 2026 09:43:17 +0100 X-Mailing-List: linux-fsdevel@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 18/47] mm/khugepaged: check if PTE table is empty in try_collapse_pte_mapped_thp() To: Baolin Wang , Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Muhammad Usama Anjum References: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> <20261031-fixes_core-v3-18-d6437171ecc3@kernel.org> <62268831-f6f3-4666-a32f-a77546b95432@linux.alibaba.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: <62268831-f6f3-4666-a32f-a77546b95432@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 11/2/26 09:20, Baolin Wang wrote: > > > On 10/31/26 5:39 PM, David Hildenbrand (Arm) wrote: >> The existing code is rather horrible and already resulted in bugs in the >> past: we special-case UFFD inserting anonymous folios by grabbing the PMD >> lock early, but ignore any other markers (guard, poison through uffd) that >> could have been inserted into the page table in the meantime, effectively >> dropping them. >> >> Let's just unify and simplify the locking: try to grab the PMD table >> lock and if that fails, flush the TLB, drop the PTE lock, take PT locks in >> the right order and check if the page table is still empty. >> >> We still perform the heavy lifting (zapping the folio ptes) under PTE table >> lock only. >> >> Include for now, as x86's flush_tlb_range() macro >> depends on hugetlb helpers. This dependency needs a separate cleanup. >> >> Both issues this fixes are rather corner cases. Let's not CC stable for >> now. >> >> Fixes: f807123d578d ("mm: allow guard regions in file-backed and read-only >> mappings") >> Fixes: 1043173eb5eb ("mm/khugepaged: collapse_pte_mapped_thp() with >> mmap_read_lock()") >> Tested-by: Gregory Price (Meta) >> Reviewed-by: Gregory Price (Meta) >> Tested-by: Muhammad Usama Anjum >> Signed-off-by: David Hildenbrand (Arm) >> --- >>   mm/khugepaged.c | 64 ++++++++++++++++++++++++++++----------------------------- >>   1 file changed, 31 insertions(+), 33 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index ce794d9760a87..ad07c8caa3bd9 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -10,6 +10,7 @@ >>   #include >>   #include >>   #include >> +#include >>   #include >>   #include >>   #include >> @@ -1832,6 +1833,17 @@ static enum scan_result set_huge_pmd(struct >> vm_area_struct *vma, unsigned long a >>       return SCAN_SUCCEED; >>   } >>   +static bool pte_table_empty(pte_t *pte) >> +{ >> +    int i; >> + >> +    for (i = 0; i < HPAGE_PMD_NR; i++, pte++) { > > Using PTRS_PER_PTE to iterate PTEs seems more straightforward? Otherwise LGTM. The difference currently shouldn't matter. I'll probably leave it as is for no such that I can move forward with upstreaming them soonish (having the code as is in -next for a couple of days). But this might be reasonable to clean up alter, thanks! -- Cheers, David