linux-kernel - Re: [Xen-devel] maybe revert commit c275a57f5ec3 "xen/balloon: Set balloon's initial state to number of existing RAM pages"

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Date:   Fri, 7 Jul 2017 20:59:58 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Jan Beulich <JBeulich@...e.com>,
        Dan Streetman <dan.streetman@...onical.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] maybe revert commit c275a57f5ec3 "xen/balloon: Set
 balloon's initial state to number of existing RAM pages"

On Tue, Mar 28, 2017 at 05:30:24PM +0200, 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, <boris.ostrovsky@...cle.com> 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.

Did we ever come with a patch for this?