Re: [PATCH v3] xen/balloon: don't online new memory initially

From: Boris Ostrovsky
Date: Tue Jul 18 2017 - 12:07:34 EST


On 07/10/2017 04:10 AM, Juergen Gross wrote:
> When setting up the Xenstore watch for the memory target size the new
> watch will fire at once. Don't try to reach the configured target size
> by onlining new memory in this case, as the current memory size will
> be smaller in almost all cases due to e.g. BIOS reserved pages.
>
> Onlining new memory will lead to more problems e.g. undesired conflicts
> with NVMe devices meant to be operated as block devices.
>
> Instead remember the difference between target size and current size
> when the watch fires for the first time and apply it to any further
> size changes, too.

I don't think I understand how deferring setting the target until next
watch firing will help with the original problem. Could you explain?

Thanks.
-boris


>
> In order to avoid races between balloon.c and xen-balloon.c init calls
> do the xen-balloon.c initialization from balloon.c.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> drivers/xen/balloon.c | 3 +++
> drivers/xen/xen-balloon.c | 22 ++++++++++++----------
> include/xen/balloon.h | 8 ++++++++
> 3 files changed, 23 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 50dcb68d8070..ab609255a0f3 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -780,6 +780,9 @@ static int __init balloon_init(void)
> }
> #endif
>
> + /* Init the xen-balloon driver. */
> + xen_balloon_init();
> +
> return 0;
> }
> subsys_initcall(balloon_init);
> diff --git a/drivers/xen/xen-balloon.c b/drivers/xen/xen-balloon.c
> index e7715cb62eef..e89136ab851e 100644
> --- a/drivers/xen/xen-balloon.c
> +++ b/drivers/xen/xen-balloon.c
> @@ -59,6 +59,8 @@ static void watch_target(struct xenbus_watch *watch,
> {
> unsigned long long new_target;
> int err;
> + static bool watch_fired;
> + static long target_diff;
>
> err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
> if (err != 1) {
> @@ -69,7 +71,14 @@ static void watch_target(struct xenbus_watch *watch,
> /* The given memory/target value is in KiB, so it needs converting to
> * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
> */
> - balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
> + new_target >>= PAGE_SHIFT - 10;
> + if (watch_fired) {
> + balloon_set_new_target(new_target - target_diff);
> + return;
> + }
> +
> + watch_fired = true;
> + target_diff = new_target - balloon_stats.target_pages;
> }
> static struct xenbus_watch target_watch = {
> .node = "memory/target",
> @@ -94,22 +103,15 @@ static struct notifier_block xenstore_notifier = {
> .notifier_call = balloon_init_watcher,
> };
>
> -static int __init balloon_init(void)
> +void xen_balloon_init(void)
> {
> - if (!xen_domain())
> - return -ENODEV;
> -
> - pr_info("Initialising balloon driver\n");
> -
> register_balloon(&balloon_dev);
>
> register_xen_selfballooning(&balloon_dev);
>
> register_xenstore_notifier(&xenstore_notifier);
> -
> - return 0;
> }
> -subsys_initcall(balloon_init);
> +EXPORT_SYMBOL_GPL(xen_balloon_init);
>
> #define BALLOON_SHOW(name, format, args...) \
> static ssize_t show_##name(struct device *dev, \
> diff --git a/include/xen/balloon.h b/include/xen/balloon.h
> index d1767dfb0d95..8906361bb50c 100644
> --- a/include/xen/balloon.h
> +++ b/include/xen/balloon.h
> @@ -35,3 +35,11 @@ static inline int register_xen_selfballooning(struct device *dev)
> return -ENOSYS;
> }
> #endif
> +
> +#ifdef CONFIG_XEN_BALLOON
> +void xen_balloon_init(void);
> +#else
> +static inline void xen_balloon_init(void)
> +{
> +}
> +#endif