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Date: Mon, 27 Dec 2010 10:08:47 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Daniel Kiper <dkiper@...-space.pl>
Cc: 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,
xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH 2/3] drivers/xen/balloon.c: Various balloon features
and fixes
On Mon, Dec 20, 2010 at 02:47:24PM +0100, Daniel Kiper wrote:
> Features and fixes:
> - HVM mode is supported now,
> - migration from mod_timer() to schedule_delayed_work(),
> - removal of driver_pages (I do not have seen any
> references to it),
> - protect before CPU exhaust by event/x process during
> errors by adding some delays in scheduling next event,
> - some other minor fixes.
>
> Signed-off-by: Daniel Kiper <dkiper@...-space.pl>
> ---
> arch/x86/xen/mmu.c | 3 +-
> drivers/xen/balloon.c | 128 +++++++++++++++++++++++++++++++++----------------
> 2 files changed, 87 insertions(+), 44 deletions(-)
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 42086ac..6278650 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -75,8 +75,7 @@
>
> /*
> * Protects atomic reservation decrease/increase against concurrent increases.
> - * Also protects non-atomic updates of current_pages and driver_pages, and
> - * balloon lists.
> + * Also protects non-atomic updates of current_pages and balloon lists.
> */
> DEFINE_SPINLOCK(xen_reservation_lock);
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 500290b..06dbdad 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -69,14 +69,11 @@ struct balloon_stats {
> /* We aim for 'current allocation' == 'target allocation'. */
> unsigned long current_pages;
> unsigned long target_pages;
> - /*
> - * Drivers may alter the memory reservation independently, but they
> - * must inform the balloon driver so we avoid hitting the hard limit.
> - */
> - unsigned long driver_pages;
> /* 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);
> @@ -103,15 +100,14 @@ static LIST_HEAD(ballooned_pages);
>
> /* Main work function, always executed in process context. */
> static void balloon_process(struct work_struct *work);
> -static DECLARE_WORK(balloon_worker, balloon_process);
> -static struct timer_list balloon_timer;
> +static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
>
> /* When ballooning out (allocating memory to return to Xen) we don't really
> want the kernel to try too hard since that can trigger the oom killer. */
> #define GFP_BALLOON \
> (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
>
> -static void scrub_page(struct page *page)
> +static inline void scrub_page(struct page *page)
> {
> #ifdef CONFIG_XEN_SCRUB_PAGES
> clear_highpage(page);
> @@ -172,9 +168,29 @@ static struct page *balloon_next_page(struct page *page)
> return list_entry(next, struct page, lru);
> }
>
> -static void balloon_alarm(unsigned long unused)
> +static void update_schedule_delay(int cmd)
> {
> - schedule_work(&balloon_worker);
> + unsigned long new_schedule_delay;
> +
> + /*
> + * cmd >= 0: balloon_stats.schedule_delay = 1,
> + * cmd < 0: increase balloon_stats.schedule_delay but
> + * no more than balloon_stats.max_schedule_delay.
> + */
> +
> + if (cmd >= 0) {
> + 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)
> @@ -191,9 +207,9 @@ static unsigned long current_target(void)
>
> static int increase_reservation(unsigned long nr_pages)
> {
> + int rc, state = 0;
> unsigned long pfn, i, flags;
> struct page *page;
> - long rc;
> struct xen_memory_reservation reservation = {
> .address_bits = 0,
> .extent_order = 0,
> @@ -206,8 +222,17 @@ static int increase_reservation(unsigned long nr_pages)
> spin_lock_irqsave(&xen_reservation_lock, flags);
>
> page = balloon_first_page();
> +
> + if (!page) {
> + state = -ENOMEM;
> + goto out;
> + }
> +
> 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);
> }
> @@ -215,8 +240,11 @@ 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) {
> + state = (rc <= 0) ? -ENOMEM : 1;
> + if (rc <= 0)
> + goto out;
> + }
>
> for (i = 0; i < rc; i++) {
> page = balloon_retrieve();
> @@ -229,7 +257,7 @@ static int increase_reservation(unsigned long nr_pages)
> set_phys_to_machine(pfn, frame_list[i]);
>
> /* Link back into the page tables if not highmem. */
> - if (pfn < max_low_pfn) {
> + if (xen_pv_domain() && !PageHighMem(page)) {
> int ret;
> ret = HYPERVISOR_update_va_mapping(
> (unsigned long)__va(pfn << PAGE_SHIFT),
> @@ -249,15 +277,14 @@ static int increase_reservation(unsigned long nr_pages)
> out:
> spin_unlock_irqrestore(&xen_reservation_lock, flags);
>
> - return rc < 0 ? rc : rc != nr_pages;
> + return state;
> }
>
> static int decrease_reservation(unsigned long nr_pages)
> {
> unsigned long pfn, i, flags;
> struct page *page;
> - int need_sleep = 0;
> - int ret;
> + int ret, state = 0;
> struct xen_memory_reservation reservation = {
> .address_bits = 0,
> .extent_order = 0,
> @@ -270,7 +297,7 @@ 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 = -ENOMEM;
> break;
> }
>
> @@ -279,7 +306,7 @@ static int decrease_reservation(unsigned long nr_pages)
>
> scrub_page(page);
>
> - if (!PageHighMem(page)) {
> + if (xen_pv_domain() && !PageHighMem(page)) {
> ret = HYPERVISOR_update_va_mapping(
> (unsigned long)__va(pfn << PAGE_SHIFT),
> __pte_ma(0), 0);
> @@ -310,7 +337,7 @@ static int decrease_reservation(unsigned long nr_pages)
>
> spin_unlock_irqrestore(&xen_reservation_lock, flags);
>
> - return need_sleep;
> + return state;
> }
>
> /*
> @@ -321,27 +348,41 @@ static int decrease_reservation(unsigned long nr_pages)
> */
> static void balloon_process(struct work_struct *work)
> {
> - int need_sleep = 0;
> + int rc, state = 0;
> 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);
> +
> + /*
> + * state > 0: hungry,
> + * state == 0: done or nothing to do,
> + * state < 0: error, go to sleep.
Would it be better to just have #defines for this?
> + */
> +
> + if (credit > 0) {
> + rc = increase_reservation(credit);
> + state = (rc < 0) ? rc : state;
> + }
> +
> + if (credit < 0) {
> + rc = decrease_reservation(-credit);
> + state = (rc < 0) ? rc : state;
> + }
> +
> + update_schedule_delay(state);
>
> #ifndef CONFIG_PREEMPT
> if (need_resched())
> schedule();
> #endif
> - } while ((credit != 0) && !need_sleep);
> + } while (credit && state >= 0);
>
> /* Schedule more work if there is some still to be done. */
> - if (current_target() != balloon_stats.current_pages)
> - mod_timer(&balloon_timer, jiffies + HZ);
> + if (state < 0)
> + schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
>
> mutex_unlock(&balloon_mutex);
> }
> @@ -351,7 +392,7 @@ static void balloon_set_new_target(unsigned long target)
> {
> /* No need for lock. Not read-modify-write updates. */
> balloon_stats.target_pages = target;
> - schedule_work(&balloon_worker);
> + schedule_delayed_work(&balloon_worker, 0);
> }
>
> static struct xenbus_watch target_watch =
> @@ -395,28 +436,28 @@ static struct notifier_block xenstore_notifier;
>
> static int __init balloon_init(void)
> {
> - unsigned long pfn;
> + unsigned long pfn, nr_pages;
> struct page *page;
>
> - if (!xen_pv_domain())
> + if (!xen_domain())
> return -ENODEV;
>
> pr_info("xen_balloon: Initialising balloon driver.\n");
>
> - balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
> + nr_pages = xen_pv_domain() ? xen_start_info->nr_pages : max_pfn;
> +
> + balloon_stats.current_pages = min(nr_pages, max_pfn);
> balloon_stats.target_pages = balloon_stats.current_pages;
> balloon_stats.balloon_low = 0;
> balloon_stats.balloon_high = 0;
> - balloon_stats.driver_pages = 0UL;
>
> - init_timer(&balloon_timer);
> - balloon_timer.data = 0;
> - balloon_timer.function = balloon_alarm;
> + balloon_stats.schedule_delay = 1;
> + balloon_stats.max_schedule_delay = 32;
How did you arrive at that number?
>
> register_balloon(&balloon_sysdev);
>
> /* Initialise the balloon with excess memory space. */
> - for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) {
> + for (pfn = nr_pages; pfn < max_pfn; pfn++) {
> page = pfn_to_page(pfn);
> if (!PageReserved(page))
> balloon_append(page);
> @@ -452,7 +493,9 @@ module_exit(balloon_exit);
> 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));
> -BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
> +
> +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)
> @@ -515,23 +558,24 @@ 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[] = {
> &attr_current_kb.attr,
> &attr_low_kb.attr,
> &attr_high_kb.attr,
> - &attr_driver_kb.attr,
> NULL
> };
>
> static struct attribute_group balloon_info_group = {
> .name = "info",
> - .attrs = balloon_info_attrs,
> + .attrs = balloon_info_attrs
> };
>
> static struct sysdev_class balloon_sysdev_class = {
> - .name = BALLOON_CLASS_NAME,
> + .name = BALLOON_CLASS_NAME
> };
>
> static int register_balloon(struct sys_device *sysdev)
> --
> 1.4.4.4
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