Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752900AbdC1Qc4 (ORCPT ); Tue, 28 Mar 2017 12:32:56 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:17578 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751711AbdC1Qcy (ORCPT ); Tue, 28 Mar 2017 12:32:54 -0400 Subject: Re: [Xen-devel] maybe revert commit c275a57f5ec3 "xen/balloon: Set balloon's initial state to number of existing RAM pages" To: Juergen Gross , 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: Boris Ostrovsky Message-ID: <95e0062c-ed5d-8a27-73ef-e94a9268467e@oracle.com> Date: Tue, 28 Mar 2017 12:32:41 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2092 Lines: 44 On 03/28/2017 11:30 AM, Juergen Gross wrote: > 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. We could indeed base calculation on initial state of e820 and not count the holes toward ballooning needs. I am not sure this will work for memory unplug though, where a hole can be created in the map and we will be supposed to handle disappearing memory via ballooning. Or am I creating a problem where none exists? -boris