Re: [PATCH] drivers: xen: deaggressive selfballoon driver

From: Konrad Rzeszutek Wilk
Date: Mon Jan 27 2014 - 10:57:57 EST


On Wed, Jan 22, 2014 at 02:57:44PM +0800, Bob Liu wrote:
> Current xen-selfballoon driver is too aggressive which may cause OOM be
> triggered more often. Eg. this bug reported by James:
> https://lkml.org/lkml/2013/11/21/158
>
> There are two mainly reasons:
> 1) The original goal_page didn't consider some pages used by kernel space, like
> slab pages and pages used by device drivers.
>
> 2) The balloon driver may not give back memory to guest OS fast enough when the
> workload suddenly aquries a lot of physical memory.
>
> In both cases, the guest OS will suffer from memory pressure and OOM may
> be triggered.
>
> The fix is make xen-selfballoon driver not that aggressive by adding extra 10%
> of total ram pages to goal_page.
> It's more valuable to keep the guest system reliable and response faster than
> balloon out these 10% pages to XEN.
>
> Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>

Looks OK to me.
> ---
> drivers/xen/xen-selfballoon.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/drivers/xen/xen-selfballoon.c b/drivers/xen/xen-selfballoon.c
> index 21e18c1..745ad79 100644
> --- a/drivers/xen/xen-selfballoon.c
> +++ b/drivers/xen/xen-selfballoon.c
> @@ -175,6 +175,7 @@ static void frontswap_selfshrink(void)
> #endif /* CONFIG_FRONTSWAP */
>
> #define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
> +#define PAGES2MB(pages) ((pages) >> (20 - PAGE_SHIFT))
>
> /*
> * Use current balloon size, the goal (vm_committed_as), and hysteresis
> @@ -525,6 +526,7 @@ EXPORT_SYMBOL(register_xen_selfballooning);
> int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
> {
> bool enable = false;
> + unsigned long reserve_pages;
>
> if (!xen_domain())
> return -ENODEV;
> @@ -549,6 +551,26 @@ int xen_selfballoon_init(bool use_selfballooning, bool use_frontswap_selfshrink)
> if (!enable)
> return -ENODEV;
>
> + /*
> + * Give selfballoon_reserved_mb a default value(10% of total ram pages)
> + * to make selfballoon not so aggressive.
> + *
> + * There are mainly two reasons:
> + * 1) The original goal_page didn't consider some pages used by kernel
> + * space, like slab pages and memory used by device drivers.
> + *
> + * 2) The balloon driver may not give back memory to guest OS fast
> + * enough when the workload suddenly aquries a lot of physical memory.
> + *
> + * In both cases, the guest OS will suffer from memory pressure and
> + * OOM killer may be triggered.
> + * By reserving extra 10% of total ram pages, we can keep the system
> + * much more reliably and response faster in some cases.
> + */
> + if (!selfballoon_reserved_mb) {
> + reserve_pages = totalram_pages / 10;
> + selfballoon_reserved_mb = PAGES2MB(reserve_pages);
> + }
> schedule_delayed_work(&selfballoon_worker, selfballoon_interval * HZ);
>
> return 0;
> --
> 1.7.10.4
>
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