Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753662AbbHRRXl (ORCPT ); Tue, 18 Aug 2015 13:23:41 -0400 Received: from mail-vk0-f46.google.com ([209.85.213.46]:36183 "EHLO mail-vk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752430AbbHRRXj (ORCPT ); Tue, 18 Aug 2015 13:23:39 -0400 MIME-Version: 1.0 In-Reply-To: <20150818165532.GA7424@gmail.com> 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> <20150814220605.GB3265@gmail.com> <20150817214554.GA5976@gmail.com> <20150818165532.GA7424@gmail.com> Date: Tue, 18 Aug 2015 10:23:38 -0700 Message-ID: Subject: Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory" From: Dan Williams To: Jerome Glisse Cc: "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" , Christoph Hellwig Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2130 Lines: 40 On Tue, Aug 18, 2015 at 9:55 AM, Jerome Glisse wrote: > On Mon, Aug 17, 2015 at 05:46:43PM -0700, Dan Williams wrote: >> On Mon, Aug 17, 2015 at 2:45 PM, Jerome Glisse wrote: >> > On Fri, Aug 14, 2015 at 07:11:27PM -0700, Dan Williams wrote: >> >> Although it does not offer perfect protection if device memory is at a >> >> physically lower address than RAM, skipping the update of these >> >> variables does seem to be what we want. For example /dev/mem would >> >> fail to allow write access to persistent memory if it fails a >> >> valid_phys_addr_range() check. Since /dev/mem does not know how to >> >> write to PMEM in a reliably persistent way, it should not treat a >> >> PMEM-pfn like RAM. >> > >> > So i attach is a patch that should keep ZONE_DEVICE out of consideration >> > for the buddy allocator. You might also want to keep page reserved and not >> > free inside the zone, you could replace the generic_online_page() using >> > set_online_page_callback() while hotpluging device memory. >> > >> >> Hmm, are we already protected by the fact that ZONE_DEVICE is not >> represented in the GFP_ZONEMASK? > > Yeah seems you right, high_zoneidx (which is derive using gfp_zone()) will > always limit which zones are considered. I thought that under memory presure > it would go over all of the zonelist entry and eventualy consider the device > zone. But it doesn't seems to be that way. > > Keeping the device zone out of the zonelist might still be a good idea, if > only to avoid pointless iteration for the page allocator. Unless someone can > think of a reason why this would be bad. > The other question I have is whether disabling ZONE_DMA is a realistic tradeoff for enabling ZONE_DEVICE? I.e. can ZONE_DMA default to off going forward, lose some ISA device support, or do we need to figure out how to enable > 4 zones. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/