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Date: Thu, 10 Feb 2011 10:51:42 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Daniel Kiper <dkiper@...-space.pl>
Cc: ian.campbell@...rix.com, akpm@...ux-foundation.org,
andi.kleen@...el.com, haicheng.li@...ux.intel.com,
fengguang.wu@...el.com, jeremy@...p.org,
dan.magenheimer@...cle.com, v.tolstov@...fip.ru, pasik@....fi,
dave@...ux.vnet.ibm.com, wdauchy@...il.com, rientjes@...gle.com,
xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH R3 5/7] xen/balloon: Protect against CPU exhaust by
event/x proces
On Thu, Feb 03, 2011 at 05:28:51PM +0100, Daniel Kiper wrote:
> Protect against CPU exhaust by event/x process during
> errors by adding some delays in scheduling next event.
>
> Signed-off-by: Daniel Kiper <dkiper@...-space.pl>
> ---
> drivers/xen/balloon.c | 99 +++++++++++++++++++++++++++++++++++++++---------
> 1 files changed, 80 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 4223f64..ed103d4 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -66,6 +66,20 @@
>
> #define BALLOON_CLASS_NAME "xen_memory"
>
> +/*
> + * balloon_process() state:
> + *
> + * BP_ERROR: error, go to sleep,
> + * BP_DONE: done or nothing to do,
> + * BP_HUNGRY: hungry.
> + */
> +
> +enum bp_state {
> + BP_ERROR,
BP_EAGAIN?
So if we fail to increase the first hour, we would keep on trying to
increase forever (with a 32 second delay between each call). Do you
think it makes sense (as a future patch, not tied in with this patchset)
to printout a printk(KERN_INFO that we have been trying to increase
for the last X hours, seconds and have not gone anywhere (and perhaps
stop trying to allocate more memory?).
> + BP_DONE,
> + BP_HUNGRY
> +};
> +
> struct balloon_stats {
> /* We aim for 'current allocation' == 'target allocation'. */
> unsigned long current_pages;
> @@ -73,6 +87,8 @@ struct balloon_stats {
> /* Number of pages in high- and low-memory balloons. */
> unsigned long balloon_low;
> unsigned long balloon_high;
> + unsigned long schedule_delay;
> + unsigned long max_schedule_delay;
> };
>
> static DEFINE_MUTEX(balloon_mutex);
> @@ -171,6 +187,25 @@ static struct page *balloon_next_page(struct page *page)
> return list_entry(next, struct page, lru);
> }
>
> +static void update_schedule_delay(enum bp_state state)
> +{
> + unsigned long new_schedule_delay;
> +
> + if (state != BP_ERROR) {
> + balloon_stats.schedule_delay = 1;
> + return;
> + }
> +
> + new_schedule_delay = balloon_stats.schedule_delay << 1;
> +
> + if (new_schedule_delay > balloon_stats.max_schedule_delay) {
> + balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
> + return;
> + }
> +
> + balloon_stats.schedule_delay = new_schedule_delay;
> +}
> +
> static unsigned long current_target(void)
> {
> unsigned long target = balloon_stats.target_pages;
> @@ -183,11 +218,12 @@ static unsigned long current_target(void)
> return target;
> }
>
> -static int increase_reservation(unsigned long nr_pages)
> +static enum bp_state increase_reservation(unsigned long nr_pages)
> {
> + enum bp_state state = BP_DONE;
> + int rc;
> unsigned long pfn, i;
> struct page *page;
> - long rc;
> struct xen_memory_reservation reservation = {
> .address_bits = 0,
> .extent_order = 0,
> @@ -198,8 +234,15 @@ static int increase_reservation(unsigned long nr_pages)
> nr_pages = ARRAY_SIZE(frame_list);
>
> page = balloon_first_page();
> +
> + if (!page)
> + return BP_ERROR;
> +
> for (i = 0; i < nr_pages; i++) {
> - BUG_ON(page == NULL);
> + if (!page) {
> + nr_pages = i;
> + break;
> + }
> frame_list[i] = page_to_pfn(page);
> page = balloon_next_page(page);
> }
> @@ -207,8 +250,11 @@ static int increase_reservation(unsigned long nr_pages)
> set_xen_guest_handle(reservation.extent_start, frame_list);
> reservation.nr_extents = nr_pages;
> rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
> - if (rc < 0)
> - goto out;
> + if (rc < nr_pages) {
> + if (rc <= 0)
> + return BP_ERROR;
> + state = BP_HUNGRY;
> + }
>
> for (i = 0; i < rc; i++) {
> page = balloon_retrieve();
> @@ -238,15 +284,14 @@ static int increase_reservation(unsigned long nr_pages)
>
> balloon_stats.current_pages += rc;
>
> - out:
> - return rc < 0 ? rc : rc != nr_pages;
> + return state;
> }
>
> -static int decrease_reservation(unsigned long nr_pages)
> +static enum bp_state decrease_reservation(unsigned long nr_pages)
> {
> + enum bp_state state = BP_DONE;
> unsigned long pfn, i;
> struct page *page;
> - int need_sleep = 0;
> int ret;
> struct xen_memory_reservation reservation = {
> .address_bits = 0,
> @@ -260,7 +305,7 @@ static int decrease_reservation(unsigned long nr_pages)
> for (i = 0; i < nr_pages; i++) {
> if ((page = alloc_page(GFP_BALLOON)) == NULL) {
> nr_pages = i;
> - need_sleep = 1;
> + state = BP_ERROR;
> break;
> }
>
> @@ -296,7 +341,7 @@ static int decrease_reservation(unsigned long nr_pages)
>
> balloon_stats.current_pages -= nr_pages;
>
> - return need_sleep;
> + return state;
> }
>
> /*
> @@ -307,27 +352,35 @@ static int decrease_reservation(unsigned long nr_pages)
> */
> static void balloon_process(struct work_struct *work)
> {
> - int need_sleep = 0;
> + enum bp_state rc, state = BP_DONE;
> long credit;
>
> mutex_lock(&balloon_mutex);
>
> do {
> credit = current_target() - balloon_stats.current_pages;
> - if (credit > 0)
> - need_sleep = (increase_reservation(credit) != 0);
> - if (credit < 0)
> - need_sleep = (decrease_reservation(-credit) != 0);
> +
> + if (credit > 0) {
> + rc = increase_reservation(credit);
> + state = (rc == BP_ERROR) ? BP_ERROR : state;
> + }
> +
> + if (credit < 0) {
> + rc = decrease_reservation(-credit);
> + state = (rc == BP_ERROR) ? BP_ERROR : state;
> + }
> +
> + update_schedule_delay(state);
>
> #ifndef CONFIG_PREEMPT
> if (need_resched())
> schedule();
> #endif
> - } while ((credit != 0) && !need_sleep);
> + } while (credit && state != BP_ERROR);
>
> /* Schedule more work if there is some still to be done. */
> - if (current_target() != balloon_stats.current_pages)
> - schedule_delayed_work(&balloon_worker, HZ);
> + if (state == BP_ERROR)
> + schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
>
> mutex_unlock(&balloon_mutex);
> }
> @@ -394,6 +447,9 @@ static int __init balloon_init(void)
> balloon_stats.balloon_low = 0;
> balloon_stats.balloon_high = 0;
>
> + balloon_stats.schedule_delay = 1;
> + balloon_stats.max_schedule_delay = 32;
> +
> register_balloon(&balloon_sysdev);
>
> /*
> @@ -447,6 +503,9 @@ BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
> BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
> BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
>
> +static SYSDEV_ULONG_ATTR(schedule_delay, 0644, balloon_stats.schedule_delay);
> +static SYSDEV_ULONG_ATTR(max_schedule_delay, 0644, balloon_stats.max_schedule_delay);
> +
> static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
> char *buf)
> {
> @@ -508,6 +567,8 @@ static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
> static struct sysdev_attribute *balloon_attrs[] = {
> &attr_target_kb,
> &attr_target,
> + &attr_schedule_delay.attr,
> + &attr_max_schedule_delay.attr
> };
>
> static struct attribute *balloon_info_attrs[] = {
> --
> 1.5.6.5
--
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