Re: [PATCH 6/7] mm/balloon_compaction: use common page ballooning

[Rafael Aquini]

On Wed, Aug 20, 2014 at 07:05:04PM +0400, Konstantin Khlebnikov wrote:
> This patch replaces checking AS_BALLOON_MAP in page->mapping->flags
> with PageBalloon which is stored directly in the struct page.
> 
> Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@xxxxxxxxxxx>
> ---
>  include/linux/balloon_compaction.h |   85 ++----------------------------------
>  mm/Kconfig                         |    2 -
>  mm/balloon_compaction.c            |    7 +--
>  mm/compaction.c                    |    9 ++--
>  mm/migrate.c                       |    4 +-
>  mm/vmscan.c                        |    2 -
>  6 files changed, 15 insertions(+), 94 deletions(-)
> 
> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
> index 53d482e..f5fda8b 100644
> --- a/include/linux/balloon_compaction.h
> +++ b/include/linux/balloon_compaction.h
> @@ -108,77 +108,6 @@ static inline void balloon_mapping_free(struct address_space *balloon_mapping)
>  }
>  
>  /*
> - * page_flags_cleared - helper to perform balloon @page ->flags tests.
> - *
> - * As balloon pages are obtained from buddy and we do not play with page->flags
> - * at driver level (exception made when we get the page lock for compaction),
> - * we can safely identify a ballooned page by checking if the
> - * PAGE_FLAGS_CHECK_AT_PREP page->flags are all cleared.  This approach also
> - * helps us skip ballooned pages that are locked for compaction or release, thus
> - * mitigating their racy check at balloon_page_movable()
> - */
> -static inline bool page_flags_cleared(struct page *page)
> -{
> -	return !(page->flags & PAGE_FLAGS_CHECK_AT_PREP);
> -}
> -
> -/*
> - * __is_movable_balloon_page - helper to perform @page mapping->flags tests
> - */
> -static inline bool __is_movable_balloon_page(struct page *page)
> -{
> -	struct address_space *mapping = page->mapping;
> -	return !PageAnon(page) && mapping_balloon(mapping);
> -}
> -
> -/*
> - * balloon_page_movable - test page->mapping->flags to identify balloon pages
> - *			  that can be moved by compaction/migration.
> - *
> - * This function is used at core compaction's page isolation scheme, therefore
> - * most pages exposed to it are not enlisted as balloon pages and so, to avoid
> - * undesired side effects like racing against __free_pages(), we cannot afford
> - * holding the page locked while testing page->mapping->flags here.
> - *
> - * As we might return false positives in the case of a balloon page being just
> - * released under us, the page->mapping->flags need to be re-tested later,
> - * under the proper page lock, at the functions that will be coping with the
> - * balloon page case.
> - */
> -static inline bool balloon_page_movable(struct page *page)
> -{
> -	/*
> -	 * Before dereferencing and testing mapping->flags, let's make sure
> -	 * this is not a page that uses ->mapping in a different way
> -	 */
> -	if (page_flags_cleared(page) && !page_mapped(page) &&
> -	    page_count(page) == 1)
> -		return __is_movable_balloon_page(page);
> -
> -	return false;
> -}
> -
> -/*
> - * isolated_balloon_page - identify an isolated balloon page on private
> - *			   compaction/migration page lists.
> - *
> - * After a compaction thread isolates a balloon page for migration, it raises
> - * the page refcount to prevent concurrent compaction threads from re-isolating
> - * the same page. For that reason putback_movable_pages(), or other routines
> - * that need to identify isolated balloon pages on private pagelists, cannot
> - * rely on balloon_page_movable() to accomplish the task.
> - */
> -static inline bool isolated_balloon_page(struct page *page)
> -{
> -	/* Already isolated balloon pages, by default, have a raised refcount */
> -	if (page_flags_cleared(page) && !page_mapped(page) &&
> -	    page_count(page) >= 2)
> -		return __is_movable_balloon_page(page);
> -
> -	return false;
> -}
> -
> -/*
>   * balloon_page_insert - insert a page into the balloon's page list and make
>   *		         the page->mapping assignment accordingly.
>   * @page    : page to be assigned as a 'balloon page'
> @@ -192,6 +121,7 @@ static inline void balloon_page_insert(struct page *page,
>  				       struct address_space *mapping,
>  				       struct list_head *head)
>  {
> +	__SetPageBalloon(page);
>  	page->mapping = mapping;
>  	list_add(&page->lru, head);
>  }
> @@ -206,6 +136,7 @@ static inline void balloon_page_insert(struct page *page,
>   */
>  static inline void balloon_page_delete(struct page *page)
>  {
> +	__ClearPageBalloon(page);
>  	page->mapping = NULL;
>  	list_del(&page->lru);
>  }
> @@ -250,24 +181,16 @@ static inline void balloon_page_insert(struct page *page,
>  				       struct address_space *mapping,
>  				       struct list_head *head)
>  {
> +	__SetPageBalloon(page);
>  	list_add(&page->lru, head);
>  }
>  
>  static inline void balloon_page_delete(struct page *page)
>  {
> +	__ClearPageBalloon(page);
>  	list_del(&page->lru);
>  }
>  
> -static inline bool balloon_page_movable(struct page *page)
> -{
> -	return false;
> -}
> -
> -static inline bool isolated_balloon_page(struct page *page)
> -{
> -	return false;
> -}
> -
>  static inline bool balloon_page_isolate(struct page *page)
>  {
>  	return false;
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 72e0db0..e09cf0a 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -237,7 +237,7 @@ config MEMORY_BALLOON
>  config BALLOON_COMPACTION
>  	bool "Allow for balloon memory compaction/migration"
>  	def_bool y
> -	depends on COMPACTION && VIRTIO_BALLOON
> +	depends on COMPACTION && MEMORY_BALLOON
>  	help
>  	  Memory fragmentation introduced by ballooning might reduce
>  	  significantly the number of 2MB contiguous memory blocks that can be
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index 533c567..22c8e03 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -253,8 +253,7 @@ bool balloon_page_isolate(struct page *page)
>  			 * Prevent concurrent compaction threads from isolating
>  			 * an already isolated balloon page by refcount check.
>  			 */
> -			if (__is_movable_balloon_page(page) &&
> -			    page_count(page) == 2) {
> +			if (PageBalloon(page) && page_count(page) == 2) {
>  				__isolate_balloon_page(page);
>  				unlock_page(page);
>  				return true;
> @@ -275,7 +274,7 @@ void balloon_page_putback(struct page *page)
>  	 */
>  	lock_page(page);
>  
> -	if (__is_movable_balloon_page(page)) {
> +	if (PageBalloon(page)) {
>  		__putback_balloon_page(page);
>  		/* drop the extra ref count taken for page isolation */
>  		put_page(page);
> @@ -300,7 +299,7 @@ int balloon_page_migrate(struct page *newpage,
>  	 */
>  	BUG_ON(!trylock_page(newpage));
>  
> -	if (WARN_ON(!__is_movable_balloon_page(page))) {
> +	if (WARN_ON(!PageBalloon(page))) {
>  		dump_page(page, "not movable balloon page");
>  		unlock_page(newpage);
>  		return rc;
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 0653f5f..e9aeed2 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -596,11 +596,10 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
>  		 * Skip any other type of page
>  		 */
>  		if (!PageLRU(page)) {
> -			if (unlikely(balloon_page_movable(page))) {
> -				if (balloon_page_isolate(page)) {
> -					/* Successfully isolated */
> -					goto isolate_success;
> -				}
> +			if (unlikely(PageBalloon(page)) &&
> +					balloon_page_isolate(page)) {
> +				/* Successfully isolated */
> +				goto isolate_success;
>  			}
>  			continue;
>  		}
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 161d044..c35e6f2 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -92,7 +92,7 @@ void putback_movable_pages(struct list_head *l)
>  		list_del(&page->lru);
>  		dec_zone_page_state(page, NR_ISOLATED_ANON +
>  				page_is_file_cache(page));
> -		if (unlikely(isolated_balloon_page(page)))
> +		if (unlikely(PageBalloon(page)))
>  			balloon_page_putback(page);
>  		else
>  			putback_lru_page(page);
> @@ -873,7 +873,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>  		}
>  	}
>  
> -	if (unlikely(__is_movable_balloon_page(page))) {
> +	if (unlikely(PageBalloon(page))) {
>  		/*
>  		 * A ballooned page does not need any special attention from
>  		 * physical to virtual reverse mapping procedures.
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2836b53..f90f93e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1160,7 +1160,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
>  
>  	list_for_each_entry_safe(page, next, page_list, lru) {
>  		if (page_is_file_cache(page) && !PageDirty(page) &&
> -		    !isolated_balloon_page(page)) {
> +		    !PageBalloon(page)) {
>  			ClearPageActive(page);
>  			list_move(&page->lru, &clean_pages);
>  		}
> 
Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>
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