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[217.140.101.70]) by mx.google.com with ESMTP id a6si422138edt.219.2019.03.27.04.21.32 for ; Wed, 27 Mar 2019 04:21:33 -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 F305BA78; Wed, 27 Mar 2019 04:21:31 -0700 (PDT) Received: from [10.162.40.146] (p8cg001049571a15.blr.arm.com [10.162.40.146]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A8BD93F557; Wed, 27 Mar 2019 04:21:29 -0700 (PDT) Subject: Re: early_memtest() patterns To: Mike Rapoport Cc: "linux-mm@kvack.org" , Andrew Morton , Michal Hocko , Dave Hansen , Vladimir Murzin , Tony Luck , Dan Williams References: <7da922fb-5254-0d3c-ce2b-13248e37db83@arm.com> <20190326135420.GA23024@rapoport-lnx> From: Anshuman Khandual Message-ID: <2f272c22-8453-7637-f744-632e70404e61@arm.com> Date: Wed, 27 Mar 2019 16:51:28 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190326135420.GA23024@rapoport-lnx> 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: On 03/26/2019 07:24 PM, Mike Rapoport wrote: > On Tue, Mar 26, 2019 at 01:39:14PM +0530, Anshuman Khandual wrote: >> 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. > It's 'LINUXrlz' ;-) Yeah eventually figured that. Though first 16 patterns switch on/off individual bits on a given byte, there does not seem to be any order or pattern to it. Never mind, was just curious.