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 7050F3AF666; Mon, 7 Sep 2026 17:08:56 +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=1788800937; cv=none; b=cWobLN3SMzSq6kd0pFlCPKFYm2cvBta7itAc66lJ58ePVNr/AE4cY+i59wCTt7KJiUlVPr1hDJHUFSdUu+Ib1vS6gnYFU3IFgEYO77H+l/emSBFkciDfoIOvQtAouP7lqQr6w4eIKvo733CBO6b2dJNM/SUlbaRDfoHB5pRfXOw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788800937; c=relaxed/simple; bh=btc7pahP8DBBefhXLxJ2nWb1mk6pUWZslp/d2qEQ+Nk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=owY0lBTtZnmiIMbySxSDV4ccu2jw+xbWxlfgCnsNBmD1zPj1D77VCsgfY3/3RfrVFpleWo9Sud8OS6RvUtOE/iQwyn1iC4QJi7RWLB73peeHpPYqz21hfCnzED/4vQkpTMUciE1OEB7IzJG+Ery7VQbjgoCPVFb07/tS1+DfDF8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aoskVabW; 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="aoskVabW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30AAE1F00A3A; Mon, 7 Sep 2026 17:08:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788800936; bh=j7x/51HwsP9l6I4L2UsRVOYC9hBKf+rW1hZb9VZ+8mk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=aoskVabW49we9m61if+yG80C3wtGQ69YtOvFI7mW0eoHdMIHHFnJ3qaxHEKq0LFHS 5MN11lbxi667fu1q0kWnrr2xojlZU6Pjj9shKb0acrAX/MqY47KHdVM2WKpQkEsEYD rROTjv/GJeFU9O5ZZOhJqZ9cRg/LjWupTnHG/Kh0LbkCx9e2FYQdVVS4toYaMSfJPN retSexSkntzEcSaWZjSrYBmj1cWP90KvFbE8LenDGr3jPKFad9FqK6Bsfu/aM/hQ1G yo5nqG2djiu7I6W/APCdjcIAMBkZZSEhKJFQOWudMlP9DXUkR9N1NzbG9Rc1Vb0Xlk QefYvOkesgvbA== Message-ID: <42c1b1be-d176-45fd-b467-464b5b87e116@kernel.org> Date: Mon, 7 Sep 2026 19:08:48 +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 6/6] tools/testing/selftests/mm: add MAP_PRIVATE-/dev/zero merge tests To: "Lorenzo Stoakes (ARM)" , Arnd Bergmann , Greg Kroah-Hartman , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Hugh Dickins , Baolin Wang , "Matthew Wilcox (Oracle)" , Jan Kara Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260902-map-private-dev-zero-v1-0-a578c730cec7@kernel.org> <20260902-map-private-dev-zero-v1-6-a578c730cec7@kernel.org> 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: <20260902-map-private-dev-zero-v1-6-a578c730cec7@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/2/26 20:00, Lorenzo Stoakes (ARM) wrote: > Assert that MAP_PRIVATE-mapped /dev/zero mappings behave like they are > anonymous. > > We test both unfaulted and faulted/unfaulted merges - each with the regions > having page offset of 0, which would not merge if the mappings were treated > as if they were file-backed. > > With the recent change that makes them behave as pure anonymous mappings, > the merges should succeed as their page offsets are equal to their > anonymous page offsets. > > Signed-off-by: Lorenzo Stoakes (ARM) > --- > tools/testing/selftests/mm/merge.c | 104 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 104 insertions(+) > > diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c > index 52b8727b6628..7c528d470404 100644 > --- a/tools/testing/selftests/mm/merge.c > +++ b/tools/testing/selftests/mm/merge.c > @@ -1362,6 +1362,110 @@ TEST_F(merge, anon_and_page_offset_mismatch_memfd) > ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 5 * page_size); > } > > +TEST_F(merge, merge_map_private_dev_zero_unfaulted) > +{ > + struct procmap_fd *procmap = &self->procmap; > + unsigned int page_size = self->page_size; > + char *carveout = self->carveout; > + char *ptr, *ptr2; > + int fd_zero; > + > + if (access("/dev/zero", F_OK)) > + SKIP(return, "No /dev/zero."); > + fd_zero = open("/dev/zero", O_RDWR); > + ASSERT_NE(fd_zero, -1); > + > + /* > + * Map two MAP_PRIVATE-/dev/zero VMAs next to one another with offset 0 > + * each. > + * > + * With these being made truly anonymous upon mapping, they will > + * merge. If they were file-backed VMAs the page offsets would prevent > + * merge: Nit: "the" merge? You're the native speaker, so I don't know if what you have is just correct :) > + * > + * |-----||------| |-------------| > + * | ptr || ptr2 | -> | ptr | > + * |-----||------| |-------------| > + */ > + ptr = mmap(carveout, 5 * page_size, PROT_READ | PROT_WRITE, > + MAP_FIXED | MAP_PRIVATE, fd_zero, 0); > + if (ptr == MAP_FAILED) { > + close(fd_zero); > + ASSERT_TRUE(false); > + } > + ptr2 = mmap(&carveout[5 * page_size], 5 * page_size, > + PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE, fd_zero, 0); > + if (ptr2 == MAP_FAILED) { > + close(fd_zero); Is the close() really required before the ASSERT? After all, you're also not munmap'ing, so I wonder to which degree we have to clean up. So maybe this could just become a ASSERT_NE(ptr2, MAP_FAILED); Same for ptr above. You could likely also do ptr = mmap() ptr2 = mmap() close(fd_zero); ASSERT_NE(ptr, MAP_FAILED); ASSERT_NE(ptr2, MAP_FAILED); > + ASSERT_TRUE(false); > + } > + close(fd_zero); > + > + /* Assert that they merged. */ > + ASSERT_TRUE(find_vma_procmap(procmap, ptr)); > + ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr); > + ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 10 * page_size); > +} > + > +TEST_F(merge, merge_map_private_dev_zero_faulted_unfaulted) > +{ > + struct procmap_fd *procmap = &self->procmap; > + unsigned int page_size = self->page_size; > + char *carveout = self->carveout; > + char *ptr, *ptr2; > + int fd_zero; > + > + if (access("/dev/zero", F_OK)) > + SKIP(return, "No /dev/zero."); > + fd_zero = open("/dev/zero", O_RDWR); > + ASSERT_NE(fd_zero, -1); > + > + /* > + * Map a MAP_PRIVATE mapping of /dev/zero with page offset 0, then fault > + * it in: > + * > + * |-------------------------------| > + * | faulted | > + * |-------------------------------| > + */ > + ptr = mmap(carveout, 15 * page_size, PROT_READ | PROT_WRITE, > + MAP_FIXED | MAP_PRIVATE, fd_zero, 0); > + if (ptr == MAP_FAILED) { > + close(fd_zero); > + ASSERT_TRUE(false); Same question regarding cleanup requirements. The ASSERT_TRUE(false) looks a bit odd. -- Cheers, David