From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vk0-f52.google.com (mail-vk0-f52.google.com [209.85.213.52]) by kanga.kvack.org (Postfix) with ESMTP id 78F076B0038 for ; Fri, 21 Aug 2015 11:02:54 -0400 (EDT) Received: by vkd66 with SMTP id 66so31979390vkd.0 for ; Fri, 21 Aug 2015 08:02:54 -0700 (PDT) Received: from mail-vk0-f50.google.com (mail-vk0-f50.google.com. [209.85.213.50]) by mx.google.com with ESMTPS id sj6si10474283vdc.20.2015.08.21.08.02.51 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Aug 2015 08:02:53 -0700 (PDT) Received: by vkfi73 with SMTP id i73so32197037vkf.2 for ; Fri, 21 Aug 2015 08:02:51 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20150815085954.GC21033@lst.de> References: <20150813031253.36913.29580.stgit@otcpl-skl-sds-2.jf.intel.com> <20150813035005.36913.77364.stgit@otcpl-skl-sds-2.jf.intel.com> <20150814213714.GA3265@gmail.com> <20150815085954.GC21033@lst.de> Date: Fri, 21 Aug 2015 08:02:51 -0700 Message-ID: Subject: Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" From: Dan Williams Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Hellwig Cc: Jerome Glisse , "linux-kernel@vger.kernel.org" , Boaz Harrosh , Rik van Riel , "linux-nvdimm@lists.01.org" , Dave Hansen , david , Ingo Molnar , Linux MM , Ingo Molnar , Mel Gorman , "H. Peter Anvin" , Ross Zwisler , "torvalds@linux-foundation.org" , David Woodhouse [ Adding David Woodhouse ] On Sat, Aug 15, 2015 at 1:59 AM, Christoph Hellwig wrote: > On Fri, Aug 14, 2015 at 02:52:15PM -0700, Dan Williams wrote: >> The idea is that this memory is not meant to be available to the page >> allocator and should not count as new memory capacity. We're only >> hotplugging it to get struct page coverage. > > This might need a bigger audit of the max_pfn usages. I remember > architectures using it as a decisions for using IOMMUs or similar. We chatted about this at LPC yesterday. The takeaway was that the max_pfn checks that the IOMMU code does is for checking whether a device needs an io-virtual mapping to reach addresses above its DMA limit (if it can't do 64-bit DMA). Given the capacities of persistent memory it's likely that a device with this limitation already can't address all of RAM let alone PMEM. So it seems to me that updating max_pfn for PMEM hotplug does not buy us anything except a few more opportunities to confuse PMEM as typical RAM. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org