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[217.140.101.70]) by mx.google.com with ESMTP id k51si1704817edd.266.2019.03.26.01.09.19 for ; Tue, 26 Mar 2019 01:09:20 -0700 (PDT) Received-SPF: pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.101.70 as permitted sender) client-ip=217.140.101.70; Authentication-Results: mx.google.com; spf=pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D414F1596; Tue, 26 Mar 2019 01:09:18 -0700 (PDT) Received: from [10.162.41.160] (p8cg001049571a15.blr.arm.com [10.162.41.160]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 803443F614; Tue, 26 Mar 2019 01:09:16 -0700 (PDT) To: "linux-mm@kvack.org" Cc: Andrew Morton , Michal Hocko , Dave Hansen , Vladimir Murzin , Tony Luck , Dan Williams From: Anshuman Khandual Subject: early_memtest() patterns Message-ID: <7da922fb-5254-0d3c-ce2b-13248e37db83@arm.com> Date: Tue, 26 Mar 2019 13:39:14 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hello, early_memtest() is being executed on many platforms even though they dont enable CONFIG_MEMTEST by default. Just being curious how the following set of patterns got decided. Are they just random 64 bit patterns ? Or there is some particular significance to them in detecting bad memory. static u64 patterns[] __initdata = { /* The first entry has to be 0 to leave memtest with zeroed memory */ 0, 0xffffffffffffffffULL, 0x5555555555555555ULL, 0xaaaaaaaaaaaaaaaaULL, 0x1111111111111111ULL, 0x2222222222222222ULL, 0x4444444444444444ULL, 0x8888888888888888ULL, 0x3333333333333333ULL, 0x6666666666666666ULL, 0x9999999999999999ULL, 0xccccccccccccccccULL, 0x7777777777777777ULL, 0xbbbbbbbbbbbbbbbbULL, 0xddddddddddddddddULL, 0xeeeeeeeeeeeeeeeeULL, 0x7a6c7258554e494cULL, /* yeah ;-) */ }; BTW what about the last one here. Most of them got moved from x86 through the commit 63823126c221dd ("x86: memtest: add additional (regular) test patterns"). - Anshuman