From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: swiotlb detection should be memory hotplug aware ? Date: Fri, 23 Jul 2010 10:59:45 -0400 Message-ID: <20100723145945.GA31857@phenom.dumpdata.com> References: <20100721135750Z.fujita.tomonori@lab.ntt.co.jp> <1279732414.10874.6.camel@ank32.eng.vmware.com> <20100722084413I.fujita.tomonori@lab.ntt.co.jp> <20100722090329O.fujita.tomonori@lab.ntt.co.jp> <1279823680.31733.20.camel@ank32.eng.vmware.com> <20100723142208.GA4008@phenom.dumpdata.com> <4C49A83C.8070203@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from rcsinet10.oracle.com ([148.87.113.121]:43262 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757709Ab0GWPAK (ORCPT >); Fri, 23 Jul 2010 11:00:10 -0400 Content-Disposition: inline In-Reply-To: <4C49A83C.8070203@linux.intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Andi Kleen Cc: Alok Kataria , FUJITA Tomonori , "lenb@kernel.org" , "x86@kernel.org" , "linux-acpi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Petr Vandrovec On Fri, Jul 23, 2010 at 04:33:32PM +0200, Andi Kleen wrote: > > >I thought SRAT has NUMA affinity information - so for example my AMD > >desktop box has that, but it does not support hotplug capability. > > > >I think first your 'hotplug_possible' code needs to be more specific - > >not just check if SRAT exists, but also if there are swaths of memory > >that are non-populated. It would also help if there was some indication > >of whether the box truly does a hardware hotplug - is there a way to do > >this? > > The SRAT declares hotplug memory ranges in advance. And Linux > already uses this > information in the SRAT parser (just the code for doing this is a > bit dumb, I have a rewrite > somewhere) > > The only drawback is that some older systems claimed to have large > hotplug memory ranges > when they didn't actually support it. So it's better to not do > anything with a lot > of overhead. > > So yes it would be reasonable to let swiotlb (and possibly other > code sizing itself > based on memory) call into the SRAT parser and check the hotplug ranges too. > > BTW longer term swiotlb should be really more dynamic anyways and grow > and shrink on demand. I attempted this some time ago with my DMA I was thinking about this at some point. I think the first step is to make SWIOTLB use the debugfs to actually print out how much of its buffers are used - and see if the 64MB is a good fit. The shrinking part scares me - I think it might be more prudent to first explore on how to grow it. The big problem looks to allocate a physical contiguity set of pages. And I guess SWIOTLB would need to change from using one big region to something of a pool system? > allocator patchkit, > unfortunately that didn't go forward. I wasn't present at that time so I don't know what the issues were - you wouldn't have a link to LKML for this?