Re: [RFCv3 3/5] mm/balloon: apply mobile page migratable into balloon

[Michael S. Tsirkin]

On Tue, Jul 07, 2015 at 01:36:23PM +0900, Gioh Kim wrote:
> From: Gioh Kim <gurugio@xxxxxxxxxxx>
> 
> Apply mobile page migration into balloon driver.
> The balloong driver has an anonymous inode that manages
> address_space_operation for page migration.
> 
> Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx>
> ---
>  drivers/virtio/virtio_balloon.c    |  3 ++
>  include/linux/balloon_compaction.h | 15 +++++++--
>  mm/balloon_compaction.c            | 65 +++++++++++++-------------------------
>  mm/compaction.c                    |  2 +-
>  mm/migrate.c                       |  2 +-
>  5 files changed, 39 insertions(+), 48 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 82e80e0..ef5b9b5 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -30,6 +30,7 @@
>  #include <linux/balloon_compaction.h>
>  #include <linux/oom.h>
>  #include <linux/wait.h>
> +#include <linux/anon_inodes.h>
>  
>  /*
>   * Balloon device works in 4K page units.  So each page is pointed to by
> @@ -505,6 +506,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
>  	balloon_devinfo_init(&vb->vb_dev_info);
>  #ifdef CONFIG_BALLOON_COMPACTION
>  	vb->vb_dev_info.migratepage = virtballoon_migratepage;
> +	vb->vb_dev_info.inode = anon_inode_new();
> +	vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
>  #endif
>  
>  	err = init_vqs(vb);
> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
> index 9b0a15d..a9e0bde 100644
> --- a/include/linux/balloon_compaction.h
> +++ b/include/linux/balloon_compaction.h
> @@ -48,6 +48,7 @@
>  #include <linux/migrate.h>
>  #include <linux/gfp.h>
>  #include <linux/err.h>
> +#include <linux/fs.h>
>  
>  /*
>   * Balloon device information descriptor.
> @@ -62,6 +63,7 @@ struct balloon_dev_info {
>  	struct list_head pages;		/* Pages enqueued & handled to Host */
>  	int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
>  			struct page *page, enum migrate_mode mode);
> +	struct inode *inode;
>  };
>  
>  extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
> @@ -73,12 +75,16 @@ static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
>  	spin_lock_init(&balloon->pages_lock);
>  	INIT_LIST_HEAD(&balloon->pages);
>  	balloon->migratepage = NULL;
> +	balloon->inode = NULL;
>  }
>  
>  #ifdef CONFIG_BALLOON_COMPACTION
> -extern bool balloon_page_isolate(struct page *page);
> +extern const struct address_space_operations balloon_aops;
> +extern bool balloon_page_isolate(struct page *page,
> +				 isolate_mode_t mode);
>  extern void balloon_page_putback(struct page *page);
> -extern int balloon_page_migrate(struct page *newpage,
> +extern int balloon_page_migrate(struct address_space *mapping,
> +				struct page *newpage,
>  				struct page *page, enum migrate_mode mode);
>  
>  /*
> @@ -124,6 +130,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
>  				       struct page *page)
>  {
>  	__SetPageBalloon(page);
> +	page->mapping = balloon->inode->i_mapping;
>  	SetPagePrivate(page);
>  	set_page_private(page, (unsigned long)balloon);
>  	list_add(&page->lru, &balloon->pages);
> @@ -140,6 +147,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
>  static inline void balloon_page_delete(struct page *page)
>  {
>  	__ClearPageBalloon(page);
> +	page->mapping = NULL;
>  	set_page_private(page, 0);
>  	if (PagePrivate(page)) {
>  		ClearPagePrivate(page);

Order of cleanup here is not the reverse of the order of initialization.
Better make it exactly the reverse.


Also, I have a question: is it enough to lock the page to make changing
the mapping safe? Do all users lock the page too?




> @@ -191,7 +199,8 @@ static inline bool isolated_balloon_page(struct page *page)
>  	return false;
>  }
>  
> -static inline bool balloon_page_isolate(struct page *page)
> +static inline bool balloon_page_isolate(struct page *page,
> +					isolate_mode_t mode)
>  {
>  	return false;
>  }
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index fcad832..0dd0b0d 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -131,43 +131,16 @@ static inline void __putback_balloon_page(struct page *page)
>  }
>  
>  /* __isolate_lru_page() counterpart for a ballooned page */
> -bool balloon_page_isolate(struct page *page)
> +bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
>  {
>  	/*
> -	 * Avoid burning cycles with pages that are yet under __free_pages(),
> -	 * or just got freed under us.
> -	 *
> -	 * In case we 'win' a race for a balloon page being freed under us and
> -	 * raise its refcount preventing __free_pages() from doing its job
> -	 * the put_page() at the end of this block will take care of
> -	 * release this page, thus avoiding a nasty leakage.
> +	 * A ballooned page, by default, has PagePrivate set.
> +	 * Prevent concurrent compaction threads from isolating
> +	 * an already isolated balloon page by clearing it.
>  	 */
> -	if (likely(get_page_unless_zero(page))) {
> -		/*
> -		 * As balloon pages are not isolated from LRU lists, concurrent
> -		 * compaction threads can race against page migration functions
> -		 * as well as race against the balloon driver releasing a page.
> -		 *
> -		 * In order to avoid having an already isolated balloon page
> -		 * being (wrongly) re-isolated while it is under migration,
> -		 * or to avoid attempting to isolate pages being released by
> -		 * the balloon driver, lets be sure we have the page lock
> -		 * before proceeding with the balloon page isolation steps.
> -		 */
> -		if (likely(trylock_page(page))) {
> -			/*
> -			 * A ballooned page, by default, has PagePrivate set.
> -			 * Prevent concurrent compaction threads from isolating
> -			 * an already isolated balloon page by clearing it.
> -			 */
> -			if (balloon_page_movable(page)) {
> -				__isolate_balloon_page(page);
> -				unlock_page(page);
> -				return true;
> -			}
> -			unlock_page(page);
> -		}
> -		put_page(page);
> +	if (balloon_page_movable(page)) {
> +		__isolate_balloon_page(page);
> +		return true;
>  	}
>  	return false;
>  }
> @@ -175,30 +148,28 @@ bool balloon_page_isolate(struct page *page)
>  /* putback_lru_page() counterpart for a ballooned page */
>  void balloon_page_putback(struct page *page)
>  {
> -	/*
> -	 * 'lock_page()' stabilizes the page and prevents races against
> -	 * concurrent isolation threads attempting to re-isolate it.
> -	 */
> -	lock_page(page);
> +	if (!isolated_balloon_page(page))
> +		return;
>  
>  	if (__is_movable_balloon_page(page)) {
>  		__putback_balloon_page(page);
> -		/* drop the extra ref count taken for page isolation */
> -		put_page(page);
>  	} else {
>  		WARN_ON(1);
>  		dump_page(page, "not movable balloon page");
>  	}
> -	unlock_page(page);
>  }
>  
>  /* move_to_new_page() counterpart for a ballooned page */
> -int balloon_page_migrate(struct page *newpage,
> +int balloon_page_migrate(struct address_space *mapping,
> +			 struct page *newpage,
>  			 struct page *page, enum migrate_mode mode)
>  {
>  	struct balloon_dev_info *balloon = balloon_page_device(page);
>  	int rc = -EAGAIN;
>  
> +	if (!isolated_balloon_page(page))
> +		return rc;
> +
>  	/*
>  	 * Block others from accessing the 'newpage' when we get around to
>  	 * establishing additional references. We should be the only one
> @@ -218,4 +189,12 @@ int balloon_page_migrate(struct page *newpage,
>  	unlock_page(newpage);
>  	return rc;
>  }
> +
> +/* define the balloon_mapping->a_ops callback to allow balloon page migration */
> +const struct address_space_operations balloon_aops = {
> +	.migratepage = balloon_page_migrate,
> +	.isolatepage = balloon_page_isolate,
> +	.putbackpage = balloon_page_putback,
> +};
> +EXPORT_SYMBOL_GPL(balloon_aops);
>  #endif /* CONFIG_BALLOON_COMPACTION */
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 018f08d..81bafaf 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -719,7 +719,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>  		 */
>  		if (!PageLRU(page)) {
>  			if (unlikely(balloon_page_movable(page))) {
> -				if (balloon_page_isolate(page)) {
> +				if (balloon_page_isolate(page, isolate_mode)) {
>  					/* Successfully isolated */
>  					goto isolate_success;
>  				}
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f53838f..c94038e 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -852,7 +852,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>  		 * in order to avoid burning cycles at rmap level, and perform
>  		 * the page migration right away (proteced by page lock).
>  		 */
> -		rc = balloon_page_migrate(newpage, page, mode);
> +		rc = balloon_page_migrate(page->mapping, newpage, page, mode);
>  		goto out_unlock;
>  	}
>  
> -- 
> 2.1.4
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