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[195.135.220.15]) by mx.google.com with ESMTPS id o7si1259870edv.140.2019.03.25.07.50.24 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Mar 2019 07:50:25 -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 058C5AF2F; Mon, 25 Mar 2019 14:50:23 +0000 (UTC) Date: Mon, 25 Mar 2019 15:50:23 +0100 From: Michal Hocko To: Jeff Moyer Cc: Dan Williams , Andrew Morton , =?iso-8859-1?B?Suly9G1l?= Glisse , Logan Gunthorpe , Toshi Kani , Vlastimil Babka , stable , Linux MM , linux-nvdimm , Linux Kernel Mailing List Subject: Re: [PATCH v5 00/10] mm: Sub-section memory hotplug support Message-ID: <20190325145023.GG9924@dhcp22.suse.cz> References: <155327387405.225273.9325594075351253804.stgit@dwillia2-desk3.amr.corp.intel.com> <20190322180532.GM32418@dhcp22.suse.cz> <20190325101945.GD9924@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Mon 25-03-19 10:28:00, Jeff Moyer wrote: > Michal Hocko writes: > > >> > and I would like to know that you are > >> > not just shifting the problem to a smaller unit and a new/creative HW > >> > will force us to go even more complicated. > >> > >> HW will not do this to us. It's software that has the problem. > >> Namespace creation is unnecessarily constrained to 128MB alignment. > > > > And why is that a problem? A lack of documentation that this is a > > requirement? Something will not work with a larger alignment? Someting > > else? > > See this email for one user-visible problem: > https://lore.kernel.org/lkml/x49imxbx22d.fsf@segfault.boston.devel.redhat.com/ : # ndctl create-namespace -m fsdax -s 128m : Error: '--size=' must align to interleave-width: 6 and alignment: 2097152 : did you intend --size=132M? : : failed to create namespace: Invalid argument So the size is in section size units. So what prevents the userspace to use a proper alignment? I am sorry if this is a stupid question but I am not really familiar with ndctl nor the pmem side of it. -- Michal Hocko SUSE Labs