From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932586AbdDGCDJ (ORCPT ); Thu, 6 Apr 2017 22:03:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49786 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753591AbdDGCC7 (ORCPT ); Thu, 6 Apr 2017 22:02:59 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 0D7C0C073D4B Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jglisse@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 0D7C0C073D4B Date: Thu, 6 Apr 2017 22:02:55 -0400 From: Jerome Glisse To: Balbir Singh Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, John Hubbard , Dan Williams , Naoya Horiguchi , David Nellans , Evgeny Baskakov , Mark Hairgrove , Sherry Cheung , Subhash Gutti Subject: Re: [HMM 14/16] mm/hmm/devmem: device memory hotplug using ZONE_DEVICE Message-ID: <20170407020254.GA13927@redhat.com> References: <20170405204026.3940-1-jglisse@redhat.com> <20170405204026.3940-15-jglisse@redhat.com> <1491529054.12351.16.camel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1491529054.12351.16.camel@gmail.com> User-Agent: Mutt/1.8.0 (2017-02-23) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Fri, 07 Apr 2017 02:02:59 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 07, 2017 at 11:37:34AM +1000, Balbir Singh wrote: > On Wed, 2017-04-05 at 16:40 -0400, Jérôme Glisse wrote: > > This introduce a simple struct and associated helpers for device driver > > to use when hotpluging un-addressable device memory as ZONE_DEVICE. It > > will find a unuse physical address range and trigger memory hotplug for > > it which allocates and initialize struct page for the device memory. > > > > Signed-off-by: Jérôme Glisse > > Signed-off-by: Evgeny Baskakov > > Signed-off-by: John Hubbard > > Signed-off-by: Mark Hairgrove > > Signed-off-by: Sherry Cheung > > Signed-off-by: Subhash Gutti > > --- > > include/linux/hmm.h | 114 +++++++++++++++ > > mm/Kconfig | 9 ++ > > mm/hmm.c | 398 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 521 insertions(+) > > > > +/* > > + * To add (hotplug) device memory, HMM assumes that there is no real resource > > + * that reserves a range in the physical address space (this is intended to be > > + * use by unaddressable device memory). It will reserve a physical range big > > + * enough and allocate struct page for it. > > I've found that the implementation of this is quite non-portable, in that > starting from iomem_resource.end+1-size (which is effectively -size) on > my platform (powerpc) does not give expected results. It could be that > additional changes are needed to arch_add_memory() to support this > use case. The CDM version does not use that part, that being said isn't -size a valid value we care only about unsigned here ? What is the end value on powerpc ? In any case this sounds more like a unsigned/signed arithmetic issue, i will look into it. > > > + > > + size = ALIGN(size, SECTION_SIZE); > > + addr = (iomem_resource.end + 1ULL) - size; > > > Why don't we allocate_resource() with the right constraints and get a new > unused region? The issue with allocate_resource() is that it does scan the resource tree from lower address to higher ones. I was told that it was less likely to have hotplug issue conflict if i pick highest physicall address for the device memory hence why i do my own scan from the end toward the start. Again all this function does not apply to PPC, it can be hidden behind x86 config if you prefer it. Cheers, Jérôme