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 C68684F68AF; Mon, 19 Oct 2026 13:37:57 +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=1792417078; cv=none; b=p7gploZtE7GGk5MW0CqWhw5cZgSK8DcRos+xZxHIs26FKAZhuzCjW0r9kOdPusv5tBzjinWX8XCxZVG5HEdgE3veClZUF+f94N42O/Fzss4axZTenoj3o+DQm3runPYv1KJjwWc2fBaOFJyCtio7vG+gra6wuTHvzkhytNFB4RM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792417078; c=relaxed/simple; bh=DkWNBP86p1Ny3thKYlcwU4OKR3uPHpisYlc604VomoQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uO/j6HVGVOHQ/yL/0f8xm1mvsEfBVITRpoReb2xHe+BZeBMK8Oe3+hRtJfrb5OypQknmgmTt5oJ/iZoFbVrFjDBGdutzuV5rZ8MtBQdDd8C0dvjqPfNhrHzFMj+wNrVv2JjdEuifBo7U7ncFVEBVQaJiJu/nLd4acHjncR+nPRU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XMX4/U2U; 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="XMX4/U2U" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AF8D91F000C6; Mon, 19 Oct 2026 13:37:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792417077; bh=KltLcIUAb/n+sPGDmQ9VfrMwiJ4IpafpRw0FqjJaXS8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=XMX4/U2UBmjjuzUmFjYnVEtJKs/hgbhAQ3E4P2BJ9BSyFgm13GtxuXVyu+m1r+TZ8 kGDtePXENyVjG0DzuYjtAdPMXyvyce9UzWDWLXQqBn9nft8MpG7MUp/tKXIBnTdnUS cMqa3M1ZLYKcuTvBUco/4YfHGnnKaNq+CqNdxW40wV2rOxugl/4hRXSls6z5OJPqmh PCTvDYMZ4bHICyb9KOezlMa4HXrUfkmb9FP646d+fRTC91gVFbWMYpL5+jNpB+US2U 6Y9/a4Y7vzJ5Wg3q96HIEzGfDSNbUhEPgaekVNS5wPE2cpiQ6yhTbwkjl11EUrhgE3 fyIKk8KOFSHXg== Message-ID: <4a6ddf56-af89-482a-b173-18e181bfc3ae@kernel.org> Date: Mon, 19 Oct 2026 15:37:52 +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] selftests/mm: keep ksm_tests on small pages To: Qiliang Yuan , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , Usama Arif , Yu Zhao , Xu Xin , Chengming Zhou , Nico Pache Cc: linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261018-bug-selftests-mm-ksm-tests-nohugepage-v1-1-55ed54bdad35@gmail.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: <20261018-bug-selftests-mm-ksm-tests-nohugepage-v1-1-55ed54bdad35@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/18/26 06:53, Qiliang Yuan wrote: > ksm_tests fills regions with identical data and checks KSM's counters > after merging them. allocate_memory() maps these regions without any > THP hint. > > With mTHP enabled the regions can be backed by large folios, which KSM > splits before merging. Splitting an anonymous folio maps its > zero-filled pages to the shared zeropage, so with use_zero_pages=0 > those pages never become KSM pages and "KSM zero page merging" fails > its count. "ksm_tests -Z -p 10 -z 0", 20 runs: > > THP setup before after > default 0/20 0/20 > every mTHP size "always" 20/20 0/20 > > Map the regions with MADV_NOHUGEPAGE, as ksm_functional_tests does. > ksm_merge_hugepages_time() maps its own THP-backed region and is not > affected. That's actually something Nico intends to fix: https://lore.kernel.org/all/20260609114619.144416-1-npache@redhat.com/ > > Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") > Signed-off-by: Qiliang Yuan > --- > tools/testing/selftests/mm/ksm_tests.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c > index 5fd7792a0d479..140ea833353b6 100644 > --- a/tools/testing/selftests/mm/ksm_tests.c > +++ b/tools/testing/selftests/mm/ksm_tests.c > @@ -178,6 +178,16 @@ static void *allocate_memory(void *ptr, int prot, int mapping, char data, size_ > ksft_perror("mmap"); > return NULL; > } > + /* > + * Splitting a large folio before merging maps its zero-filled pages > + * to the shared zeropage, so keep the pages small. Ignore EINVAL on > + * kernels without THP. > + */ > + if (madvise(map_ptr, map_size, MADV_NOHUGEPAGE) && errno != EINVAL) { > + ksft_perror("madvise"); > + munmap(map_ptr, map_size); > + return NULL; > + } > memset(map_ptr, data, map_size); > if (mprotect(map_ptr, map_size, prot)) { > ksft_perror("mprotect"); > > --- > base-commit: 90201351a862182bdabfc1ad1c97b1e1b6ed5931 > change-id: 20261016-bug-selftests-mm-ksm-tests-nohugepage-1414868db0ef > > Best regards, -- Cheers, David