Re: [RFC PATCH 3/4] kvm: Add guest side support for free memory hints

Dave Hansen
2019-02-04T19:44:32Z

On 2/4/19 10:15 AM, Alexander Duyck wrote:
> +#ifdef CONFIG_KVM_GUEST
> +#include <linux/jump_label.h>
> +extern struct static_key_false pv_free_page_hint_enabled;
> +
> +#define HAVE_ARCH_FREE_PAGE
> +void __arch_free_page(struct page *page, unsigned int order);
> +static inline void arch_free_page(struct page *page, unsigned int order)
> +{
> + if (static_branch_unlikely(&pv_free_page_hint_enabled))
> + __arch_free_page(page, order);
> +}
> +#endif

So, this ends up with at least a call, a branch and a ret added to the
order-0 paths, including freeing pages to the per-cpu-pageset lists.
That seems worrisome.

What performance testing has been performed to look into the overhead
added to those paths?