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[195.135.220.15]) by mx.google.com with ESMTPS id j7si2271167edh.246.2019.03.26.01.40.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Mar 2019 01:40:41 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 25635AD47; Tue, 26 Mar 2019 08:40:41 +0000 (UTC) Date: Tue, 26 Mar 2019 09:40:40 +0100 From: Michal Hocko To: Anshuman Khandual Cc: "linux-mm@kvack.org" , Andrew Morton , Dave Hansen , Vladimir Murzin , Tony Luck , Dan Williams Subject: Re: early_memtest() patterns Message-ID: <20190326084040.GF28406@dhcp22.suse.cz> References: <7da922fb-5254-0d3c-ce2b-13248e37db83@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7da922fb-5254-0d3c-ce2b-13248e37db83@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Tue 26-03-19 13:39:14, 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, This are setting different bit patterns, a single/two/three bit(s) at a different possition of the work. > 0x7a6c7258554e494cULL, /* yeah ;-) */ Looks like an easter egg string to me. -- Michal Hocko SUSE Labs