From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shannon Zhao Subject: Re: Design doc of adding ACPI support for arm64 on Xen - version 2 Date: Wed, 12 Aug 2015 10:42:27 +0800 Message-ID: <55CAB293.5030900@huawei.com> References: <55C413D5.7000709@huawei.com> <1439302364.9747.259.camel@citrix.com> <55CA0C0C.70403@citrix.com> <1439305140.9747.278.camel@citrix.com> <55CA1085.6050506@citrix.com> <1439306359.9747.280.camel@citrix.com> <55CA1C60.1020006@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55CA1C60.1020006@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Julien Grall , Ian Campbell , David Vrabel , xen-devel , Jan Beulich , Stefano Stabellini , Parth Dixit , Christoffer Dall , Shannon Zhao Cc: Hangaohuai , "Huangpeng (Peter)" List-Id: xen-devel@lists.xenproject.org On 2015/8/12 0:01, Julien Grall wrote: > On 11/08/15 16:19, Ian Campbell wrote: >>> IIRC we talked about it few months ago and you said that using balloon >>> page will split in 4K the 1G/2M mapping done in the stage-2 p2m. >> >> Did I? Odd because I'm also of the opinion that alloc_ballooned_pages >> should operate in chunks of 2M at the hypercall layer and keep any >> resulting spare 4K pages on a free list to use for future such allocations. > > That from what I recall from an IRL talk. > > Anyway, I've looked in my archive to see why we decided to keep the > grant table parameters (in Xen ACPI table at this point). We were not > sure that the domain as all the key in hand in order to find memory hole. > > I think it's quite important to not think only about Linux but all other > Operating Systems. If we ever require a parameters later, it would mean > that the OS won't be able to run as DOM0 on older Xen. > > Linux is using ballooned page, which means loosing ~128KB (default of > the grant table on ARM) of memory because we never give back the page to > Xen due the 1:1 mapping. Although I guess this is not a big deal as it's > quite small and Linux, as said by David, will support memory hotplug soon. > > FreeBSD is using memory hole in the address space so there is no issue here. > > So I guess we could skip this parameters as 128KB doesn't seem to be a > big deal. > >> IOW it should avoid such shattering where it can. > > That would work too. > So use xlated_setup_gnttab_pages for both DT and ACPI? -- Shannon