Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753317AbdC1Pa7 (ORCPT ); Tue, 28 Mar 2017 11:30:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:45912 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751921AbdC1Pa5 (ORCPT ); Tue, 28 Mar 2017 11:30:57 -0400 Subject: Re: [Xen-devel] maybe revert commit c275a57f5ec3 "xen/balloon: Set balloon's initial state to number of existing RAM pages" To: Boris Ostrovsky , Jan Beulich , Dan Streetman References: <0628e2af-f7e7-056a-82ec-68860f9c4f29@oracle.com> <20170324211016.GG9755@char.us.oracle.com> <9b134234-5b38-c325-b3c2-f37b4c45c2cf@oracle.com> <58DA361E0200007800148E16@prv-mh.provo.novell.com> <2288a326-752e-85a5-d986-62c86b91e249@oracle.com> Cc: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org From: Juergen Gross Message-ID: Date: Tue, 28 Mar 2017 17:30:24 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <2288a326-752e-85a5-d986-62c86b91e249@oracle.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1698 Lines: 39 On 28/03/17 16:27, Boris Ostrovsky wrote: > On 03/28/2017 04:08 AM, Jan Beulich wrote: >>>>> On 28.03.17 at 03:57, wrote: >>> I think there is indeed a disconnect between target memory (provided by >>> the toolstack) and current memory (i.e actual pages available to the guest). >>> >>> For example >>> >>> [ 0.000000] BIOS-e820: [mem 0x000000000009e000-0x000000000009ffff] >>> reserved >>> [ 0.000000] BIOS-e820: [mem 0x00000000000e0000-0x00000000000fffff] >>> reserved >>> >>> are missed in target calculation. The hvmloader marks them as RESERVED >>> (in build_e820_table()) but target value is not aware of this action. >>> >>> And then the same problem repeats when kernel removes >>> 0x000a0000-0x000fffff chunk. >> But this is all in-guest behavior, i.e. nothing an entity outside the >> guest (tool stack or hypervisor) should need to be aware of. That >> said, there is still room for improvement in the tools I think: >> Regions which architecturally aren't RAM (namely the >> 0xa0000-0xfffff range) would probably better not be accounted >> for as RAM as far as ballooning is concerned. In the hypervisor, >> otoh, all memory assigned to the guest (i.e. including such backing >> ROMs) needs to be accounted. > > On the Linux side we should not include in balloon calculations pages > reserved by trim_bios_range(), i.e. (BIOS_END-BIOS_BEGIN) + 1. > > Which leaves hvmloader's special pages (and possibly memory under > 0xA0000 which may get reserved). Can we pass this info to guests via > xenstore? I'd rather keep an internal difference between online pages and E820-map count value in the balloon driver. This should work always. Juergen