Re: [PATCH 1/4] mm: introduce compaction and migration for virtio ballooned pages

[Rafael Aquini <aquini@redhat.com>]

On Mon, Jun 25, 2012 at 07:31:38PM -0400, Konrad Rzeszutek Wilk wrote:
> On Mon, Jun 25, 2012 at 7:25 PM, Rafael Aquini <aquini@redhat.com> wrote:
> > This patch introduces helper functions that teach compaction and migration bits
> > how to cope with pages which are part of a guest memory balloon, in order to
> > make them movable by memory compaction procedures.
> >
> 
> Should the names that are exported be prefixed with kvm_?
>
I rather let them as generic as possible, specially because I believe other
balloon drivers can leverage the same technique to make their page lists movable
as well, in the near future. However, I do agree with your tip if we ended up
finding out no one else can reuse this piece of code.

 
> > Signed-off-by: Rafael Aquini <aquini@redhat.com>
> > ---
> >  include/linux/mm.h |   17 +++++++++++++
> >  mm/compaction.c    |   72 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  mm/migrate.c       |   30 +++++++++++++++++++++-
> >  3 files changed, 118 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index b36d08c..360656e 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1629,5 +1629,22 @@ static inline unsigned int debug_guardpage_minorder(void) { return 0; }
> >  static inline bool page_is_guard(struct page *page) { return false; }
> >  #endif /* CONFIG_DEBUG_PAGEALLOC */
> >
> > +#if (defined(CONFIG_VIRTIO_BALLOON) || \
> > +       defined(CONFIG_VIRTIO_BALLOON_MODULE)) && defined(CONFIG_COMPACTION)
> > +extern int is_balloon_page(struct page *);
> > +extern int isolate_balloon_page(struct page *);
> > +extern int putback_balloon_page(struct page *);
> > +
> > +/* return 1 if page is part of a guest's memory balloon, 0 otherwise */
> > +static inline int PageBalloon(struct page *page)
> > +{
> > +       return is_balloon_page(page);
> > +}
> > +#else
> > +static inline int PageBalloon(struct page *page)               { return 0; }
> > +static inline int isolate_balloon_page(struct page *page)      { return 0; }
> > +static inline int putback_balloon_page(struct page *page)      { return 0; }
> > +#endif /* (VIRTIO_BALLOON || VIRTIO_BALLOON_MODULE) && COMPACTION */
> > +
> >  #endif /* __KERNEL__ */
> >  #endif /* _LINUX_MM_H */
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index 7ea259d..8835d55 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/backing-dev.h>
> >  #include <linux/sysctl.h>
> >  #include <linux/sysfs.h>
> > +#include <linux/export.h>
> >  #include "internal.h"
> >
> >  #if defined CONFIG_COMPACTION || defined CONFIG_CMA
> > @@ -312,6 +313,14 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> >                        continue;
> >                }
> >
> > +               /*
> > +                * For ballooned pages, we need to isolate them before testing
> > +                * for PageLRU, as well as skip the LRU page isolation steps.
> > +                */
> > +               if (PageBalloon(page))
> > +                       if (isolate_balloon_page(page))
> > +                               goto isolated_balloon_page;
> > +
> >                if (!PageLRU(page))
> >                        continue;
> >
> > @@ -338,6 +347,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
> >
> >                /* Successfully isolated */
> >                del_page_from_lru_list(page, lruvec, page_lru(page));
> > +isolated_balloon_page:
> >                list_add(&page->lru, migratelist);
> >                cc->nr_migratepages++;
> >                nr_isolated++;
> > @@ -903,4 +913,66 @@ void compaction_unregister_node(struct node *node)
> >  }
> >  #endif /* CONFIG_SYSFS && CONFIG_NUMA */
> >
> > +#if defined(CONFIG_VIRTIO_BALLOON) || defined(CONFIG_VIRTIO_BALLOON_MODULE)
> > +/*
> > + * Balloon pages special page->mapping.
> > + * users must properly allocate and initiliaze an instance of balloon_mapping,
> > + * and set it as the page->mapping for balloon enlisted page instances.
> > + *
> > + * address_space_operations necessary methods for ballooned pages:
> > + *   .migratepage    - used to perform balloon's page migration (as is)
> > + *   .invalidatepage - used to isolate a page from balloon's page list
> > + *   .freepage       - used to reinsert an isolated page to balloon's page list
> > + */
> > +struct address_space *balloon_mapping;
> > +EXPORT_SYMBOL(balloon_mapping);
> > +
> > +/* ballooned page id check */
> > +int is_balloon_page(struct page *page)
> > +{
> > +       struct address_space *mapping = page->mapping;
> > +       if (mapping == balloon_mapping)
> > +               return 1;
> > +       return 0;
> > +}
> > +
> > +/* __isolate_lru_page() counterpart for a ballooned page */
> > +int isolate_balloon_page(struct page *page)
> > +{
> > +       struct address_space *mapping = page->mapping;
> > +       if (mapping->a_ops->invalidatepage) {
> > +               /*
> > +                * We can race against move_to_new_page() and stumble across a
> > +                * locked 'newpage'. If we succeed on isolating it, the result
> > +                * tends to be disastrous. So, we sanely skip PageLocked here.
> > +                */
> > +               if (likely(!PageLocked(page) && get_page_unless_zero(page))) {
> > +                       /*
> > +                        * A ballooned page, by default, has just one refcount.
> > +                        * Prevent concurrent compaction threads from isolating
> > +                        * an already isolated balloon page.
> > +                        */
> > +                       if (page_count(page) == 2) {
> > +                               mapping->a_ops->invalidatepage(page, 0);
> > +                               return 1;
> > +                       }
> > +                       /* Drop refcount taken for this already isolated page */
> > +                       put_page(page);
> > +               }
> > +       }
> > +       return 0;
> > +}
> > +
> > +/* putback_lru_page() counterpart for a ballooned page */
> > +int putback_balloon_page(struct page *page)
> > +{
> > +       struct address_space *mapping = page->mapping;
> > +       if (mapping->a_ops->freepage) {
> > +               mapping->a_ops->freepage(page);
> > +               put_page(page);
> > +               return 1;
> > +       }
> > +       return 0;
> > +}
> > +#endif /* CONFIG_VIRTIO_BALLOON || CONFIG_VIRTIO_BALLOON_MODULE */
> >  #endif /* CONFIG_COMPACTION */
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index be26d5c..ffc02a4 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -78,7 +78,10 @@ void putback_lru_pages(struct list_head *l)
> >                list_del(&page->lru);
> >                dec_zone_page_state(page, NR_ISOLATED_ANON +
> >                                page_is_file_cache(page));
> > -               putback_lru_page(page);
> > +               if (unlikely(PageBalloon(page)))
> > +                       VM_BUG_ON(!putback_balloon_page(page));
> > +               else
> > +                       putback_lru_page(page);
> >        }
> >  }
> >
> > @@ -783,6 +786,17 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> >                }
> >        }
> >
> > +       if (PageBalloon(page)) {
> > +               /*
> > +                * A ballooned page does not need any special attention from
> > +                * physical to virtual reverse mapping procedures.
> > +                * To avoid burning cycles at rmap level,
> > +                * skip attempts to unmap PTEs or remap swapcache.
> > +                */
> > +               remap_swapcache = 0;
> > +               goto skip_unmap;
> > +       }
> > +
> >        /*
> >         * Corner case handling:
> >         * 1. When a new swap-cache page is read into, it is added to the LRU
> > @@ -852,6 +866,20 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> >                        goto out;
> >
> >        rc = __unmap_and_move(page, newpage, force, offlining, mode);
> > +
> > +       if (PageBalloon(newpage)) {
> > +               /*
> > +                * A ballooned page has been migrated already. Now, it is the
> > +                * time to wrap-up counters, handle the old page back to Buddy
> > +                * and return.
> > +                */
> > +               list_del(&page->lru);
> > +               dec_zone_page_state(page, NR_ISOLATED_ANON +
> > +                                   page_is_file_cache(page));
> > +               put_page(page);
> > +               __free_page(page);
> > +               return rc;
> > +       }
> >  out:
> >        if (rc != -EAGAIN) {
> >                /*
> > --
> > 1.7.10.2
> >
> > --
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