Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752393AbdC2Egi (ORCPT ); Wed, 29 Mar 2017 00:36:38 -0400 Received: from mx2.suse.de ([195.135.220.15]:44710 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751936AbdC2Egh (ORCPT ); Wed, 29 Mar 2017 00:36:37 -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> <95e0062c-ed5d-8a27-73ef-e94a9268467e@oracle.com> Cc: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org From: Juergen Gross Message-ID: Date: Wed, 29 Mar 2017 06:36:34 +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: <95e0062c-ed5d-8a27-73ef-e94a9268467e@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: 2269 Lines: 49 On 28/03/17 18:32, Boris Ostrovsky wrote: > 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? I'm rather sure memory has to be offlined before being deleted from the E820 map. Juergen