From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4EB843E5594 for ; Mon, 18 May 2026 09:19:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779095957; cv=none; b=W+NNeemGLNGrLMDgNDV0yKdM7Tgc5JbwlluxPYMUQ+Zjf/TognGlqV8JcKruvz+grW3ME0l2ebswmEmrqAlfhmc7je9AxRmLEmyTQidXLAsz9kKOSpwnv2vsQL+SqYxQ2Q4atUelh0XW98/HSddxZImlGeoreN59JW/dPctT0/g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779095957; c=relaxed/simple; bh=DZH+aw/YsPdELqq/ZeNgILgKIH8IjEFBwfkEm5V3O5A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SDgO9vnOyLLBoKEJcjEweITZSOuBjLVExZ037MrCAFqRIgSSaua+8OPwW6XxRP7q7lNDFHQqJbzsr9I7H5LRnPA24jvLQ5faSXQJ7sUg81Ia/8S0o5OaG2u5sMA5POJmn76q+PgpOhp0x5Ht8SLDHH5uvY9+HV9OCq8wO31kUt4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DmeFjVJj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DmeFjVJj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 10D56C2BCB7; Mon, 18 May 2026 09:19:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1779095956; bh=DZH+aw/YsPdELqq/ZeNgILgKIH8IjEFBwfkEm5V3O5A=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=DmeFjVJjtefk47ml+OBCuiYk+M/deTJHfRailg4G1HPYGg9Uk0oAgtmkt+E2rgWUV UR5QxI5l/5kup/gRXBGL4QnxlcKPg/Kdc8+0e/6maJ5bMxUU9SmBOdFl7+0vuPUj0b idktPUqVpacEMef/F23Q/fEQHKaSohRCJQxIAbLDn8waNljOZAapuhO4YwM+SaNlmi jiZOjskkqYtmf111mu87RKXVxAot10n6CEyPLxSH/w//XQbKPDi2N/yaj5DyblCoFN lPcqXqb8DPw0lswaMDD5p660b8wil/wgh1bUL/T6RkXBAu4kl/D/zvDGag/c19MVt4 dQsuakRl4XunA== Message-ID: <7d54b6b1-1f22-483c-9629-0f4310ca97e3@kernel.org> Date: Mon, 18 May 2026 11:19:11 +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 v4 5/5] ksm: add mremap selftests for ksm_rmap_walk To: xu.xin16@zte.com.cn Cc: ljs@kernel.org, akpm@linux-foundation.org, hughd@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, michel@lespinasse.org References: <202605161030201132-29L7DohlwP7mqnZJRgt@zte.com.cn> 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: <202605161030201132-29L7DohlwP7mqnZJRgt@zte.com.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/16/26 04:30, xu.xin16@zte.com.cn wrote: >>> --- a/tools/testing/selftests/mm/rmap.c >>> +++ b/tools/testing/selftests/mm/rmap.c >>> @@ -430,4 +430,83 @@ TEST_F(migrate, ksm) >>> propagate_children(_metadata, data); >>> } >>> >>> +static void prepare_two_pages(struct global_data *data) >>> +{ >>> + /* Allocate exactly 2 pages for the test */ >>> + data->mapsize = 2 * getpagesize(); >>> + data->region = mmap(NULL, data->mapsize, PROT_READ | PROT_WRITE, >>> + MAP_PRIVATE | MAP_ANON, -1, 0); >>> + if (data->region == MAP_FAILED) >>> + ksft_exit_fail_perror("mmap failed"); >>> + >>> + /* Fill both pages with identical content to encourage KSM merging */ >>> + memset(data->region, 0x77, data->mapsize); >>> +} >>> + >>> +static int mremap_merge_and_migrate(struct global_data *data) >>> +{ >>> + int ret, pagemap_fd; >>> + void *old_region = data->region; >>> + unsigned long page_sz = getpagesize(); >>> + >>> + /* >>> + * Mremap the second page to the first page's location (FIXED). >>> + * This effectively overwrites the first page, leaving the second page >>> + * unmapped. The physical page originally at the second page is now >>> + * mapped at the first page's virtual address. >>> + */ >> >> >> But if there is only a single page, why should it get merged by KSM? > > This test runs in multi-threads, So there are not only one page from this thread but > also many other pages which are mergeable in all other threads. At least the test did not reveal the problem in patch #3 :) Can't we just use a single VMA (e.g., 32 pages), fill it with pages of the same content, let it merge, then mremap half of it, and then migrate a page etc? -- Cheers, David