On Fri, Jul 24, 2015 at 12:47:46PM +0100, David Vrabel wrote:
> alloc_xenballooned_pages() is used to get ballooned pages to back
> foreign mappings etc. Instead of having to balloon out real pages,
> use (if supported) hotplugged memory.
>
> This makes more memory available to the guest and reduces
> fragmentation in the p2m.
>
> If userspace is lacking a udev rule (or similar) to online hotplugged
Is that udev rule already in distros?
> regions automatically, alloc_xenballooned_pages() will timeout and
> fall back to the old behaviour of ballooning out pages.
>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Reviewed-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> ---
> drivers/xen/balloon.c | 32 ++++++++++++++++++++++++++------
> include/xen/balloon.h | 1 +
> 2 files changed, 27 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index cc68a4d..fd6970f3 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -99,6 +99,7 @@ static xen_pfn_t frame_list[PAGE_SIZE / sizeof(unsigned long)];
>
> /* List of ballooned pages, threaded through the mem_map array. */
> static LIST_HEAD(ballooned_pages);
> +static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
>
> /* Main work function, always executed in process context. */
> static void balloon_process(struct work_struct *work);
> @@ -127,6 +128,7 @@ static void __balloon_append(struct page *page)
> list_add(&page->lru, &ballooned_pages);
> balloon_stats.balloon_low++;
> }
> + wake_up(&balloon_wq);
> }
>
> static void balloon_append(struct page *page)
> @@ -253,7 +255,8 @@ static enum bp_state reserve_additional_memory(void)
> int nid, rc;
> unsigned long balloon_hotplug;
>
> - credit = balloon_stats.target_pages - balloon_stats.total_pages;
> + credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
> + - balloon_stats.total_pages;
>
> /*
> * Already hotplugged enough pages? Wait for them to be
> @@ -334,7 +337,7 @@ static struct notifier_block xen_memory_nb = {
> static enum bp_state reserve_additional_memory(void)
> {
> balloon_stats.target_pages = balloon_stats.current_pages;
> - return BP_DONE;
> + return BP_ECANCELED;
> }
> #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
>
> @@ -538,13 +541,31 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
> {
> int pgno = 0;
> struct page *page;
> +
> mutex_lock(&balloon_mutex);
> +
> + balloon_stats.target_unpopulated += nr_pages;
> +
> while (pgno < nr_pages) {
> page = balloon_retrieve(true);
> if (page) {
> pages[pgno++] = page;
> } else {
> enum bp_state st;
> +
> + st = reserve_additional_memory();
> + if (st != BP_ECANCELED) {
> + int ret;
> +
> + mutex_unlock(&balloon_mutex);
> + ret = wait_event_timeout(balloon_wq,
> + !list_empty(&ballooned_pages),
> + msecs_to_jiffies(100));
> + mutex_lock(&balloon_mutex);
> + if (ret > 0)
> + continue;
> + }
> +
> st = decrease_reservation(nr_pages - pgno, GFP_USER);
> if (st != BP_DONE)
> goto out_undo;
> @@ -553,11 +574,8 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
> mutex_unlock(&balloon_mutex);
> return 0;
> out_undo:
> - while (pgno)
> - balloon_append(pages[--pgno]);
> - /* Free the memory back to the kernel soon */
> - schedule_delayed_work(&balloon_worker, 0);
> mutex_unlock(&balloon_mutex);
> + free_xenballooned_pages(pgno, pages);
> return -ENOMEM;
> }
> EXPORT_SYMBOL(alloc_xenballooned_pages);
> @@ -578,6 +596,8 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
> balloon_append(pages[i]);
> }
>
> + balloon_stats.target_unpopulated -= nr_pages;
> +
> /* The balloon may be too large now. Shrink it if needed. */
> if (current_credit())
> schedule_delayed_work(&balloon_worker, 0);
> diff --git a/include/xen/balloon.h b/include/xen/balloon.h
> index 83efdeb..d1767df 100644
> --- a/include/xen/balloon.h
> +++ b/include/xen/balloon.h
> @@ -8,6 +8,7 @@ struct balloon_stats {
> /* We aim for 'current allocation' == 'target allocation'. */
> unsigned long current_pages;
> unsigned long target_pages;
> + unsigned long target_unpopulated;
> /* Number of pages in high- and low-memory balloons. */
> unsigned long balloon_low;
> unsigned long balloon_high;
> --
> 2.1.4
>
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