Re: [PATCH v3] xen/balloon: add late_initcall_sync() for initial ballooning done

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxxxx
> > +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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