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

[Boris Ostrovsky]

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?


-boris


> +			pr_warn_once("Initial ballooning failed, %ld pages need to be freed.\n",
> +				     -credit);
> +			if (jiffies - last_changed >=
> +			    HZ * balloon_stats.boot_timeout)
> +				panic("Initial ballooning failed!\n");
> +		}
> +