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[192.134.164.83]) by mx.google.com with ESMTPS id l19si4150510wrf.400.2019.02.12.00.11.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Feb 2019 00:11:22 -0800 (PST) Received-SPF: pass (google.com: domain of brice.goglin@inria.fr designates 192.134.164.83 as permitted sender) client-ip=192.134.164.83; Authentication-Results: mx.google.com; spf=pass (google.com: domain of brice.goglin@inria.fr designates 192.134.164.83 as permitted sender) smtp.mailfrom=Brice.Goglin@inria.fr X-IronPort-AV: E=Sophos;i="5.58,361,1544482800"; d="scan'208";a="369024966" Received: from unknown (HELO [193.50.110.170]) ([193.50.110.170]) by mail2-relais-roc.national.inria.fr with ESMTP/TLS/AES128-SHA; 12 Feb 2019 09:11:04 +0100 Subject: Re: [PATCHv4 10/13] node: Add memory caching attributes To: Keith Busch , Jonathan Cameron Cc: "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "linux-mm@kvack.org" , Greg Kroah-Hartman , Rafael Wysocki , "Hansen, Dave" , "Williams, Dan J" References: <20190116175804.30196-1-keith.busch@intel.com> <20190116175804.30196-11-keith.busch@intel.com> <4a7d1c0c-c269-d7b2-11cb-88ad62b70a06@inria.fr> <20190210171958.00003ab2@huawei.com> <20190211152303.GA4525@localhost.localdomain> From: Brice Goglin Openpgp: preference=signencrypt Autocrypt: addr=Brice.Goglin@inria.fr; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20190211152303.GA4525@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US 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: Le 11/02/2019 à 16:23, Keith Busch a écrit : > On Sun, Feb 10, 2019 at 09:19:58AM -0800, Jonathan Cameron wrote: >> On Sat, 9 Feb 2019 09:20:53 +0100 >> Brice Goglin wrote: >> >>> Hello Keith >>> >>> Could we ever have a single side cache in front of two NUMA nodes ? I >>> don't see a way to find that out in the current implementation. Would we >>> have an "id" and/or "nodemap" bitmask in the sidecache structure ? >> This is certainly a possible thing for hardware to do. >> >> ACPI IIRC doesn't provide any means of representing that - your best >> option is to represent it as two different entries, one for each of the >> memory nodes. Interesting question of whether you would then claim >> they were half as big each, or the full size. Of course, there are >> other possible ways to get this info beyond HMAT, so perhaps the interface >> should allow it to be exposed if available? > HMAT doesn't do this, but I want this interface abstracted enough from > HMAT to express whatever is necessary. > > The CPU cache is the closest existing exported attributes to this, > and they provide "shared_cpu_list". To that end, I can export a > "shared_node_list", though previous reviews strongly disliked multi-value > sysfs entries. :( > > Would shared-node symlinks capture the need, and more acceptable? As a user-space guy reading these files/symlinks, I would prefer reading a bitmask just like we do for CPU cache "cpumap" or CPU "siblings" files (or sibling_list). Reading a directory and looking for dentries matching "foo%d" is far less convenient  in C. If all these files are inside a dedicated subdirectory, it's better but still not as easy. Brice