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    SubjectRe: [PATCHv2 08/10] xen/balloon: use hotplugged pages for foreign mappings etc.
    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@citrix.com>
    > Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
    > ---
    > 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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