linux-kernel - Re: [PATCH v3] xen/balloon: add late_initcall

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Date:   Sat, 30 Oct 2021 00:18:42 +0200
From:   Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org,
        Stefano Stabellini <sstabellini@...nel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] xen/balloon: add late_initcall_sync() for initial
 ballooning done

On Fri, Oct 29, 2021 at 05:46:18PM -0400, Boris Ostrovsky wrote:
> 
> On 10/29/21 10:20 AM, Juergen Gross wrote:
> > --- a/Documentation/ABI/stable/sysfs-devices-system-xen_memory
> > +++ b/Documentation/ABI/stable/sysfs-devices-system-xen_memory
> > @@ -84,3 +84,13 @@ Description:
> >   		Control scrubbing pages before returning them to Xen for others domains
> >   		use. Can be set with xen_scrub_pages cmdline
> >   		parameter. Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
> > +
> > +What:		/sys/devices/system/xen_memory/xen_memory0/boot_timeout
> > +Date:		November 2021
> > +KernelVersion:	5.16
> > +Contact:	xen-devel@...ts.xenproject.org
> > +Description:
> > +		The time (in seconds) to wait before giving up to boot in case
> > +		initial ballooning fails to free enough memory. Applies only
> > +		when running as HVM or PVH guest and started with less memory
> > +		configured than allowed at max.
> 
> 
> How is this going to be used? We only need this during boot.
> 
> 
> > -		state = update_schedule(state);
> > +		balloon_state = update_schedule(balloon_state);
> 
> 
> Now that balloon_state has whole file scope it can probably be updated inside update_schedule().
> 
> 
> > +	while ((credit = current_credit()) < 0) {
> > +		if (credit != last_credit) {
> > +			last_changed = jiffies;
> > +			last_credit = credit;
> > +		}
> > +		if (balloon_state == BP_ECANCELED) {
> 
> 
> What about other states? We are really waiting for BP_DONE, aren't we?

BP_DONE is set also as an intermediate step:

                       balloon_state = decrease_reservation(n_pages,
                                                            GFP_BALLOON);
                       if (balloon_state == BP_DONE && n_pages != -credit &&
                            n_pages < totalreserve_pages)
                               balloon_state = BP_EAGAIN;

It would be bad to finish waiting in this case.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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