[patch 5/4] mm: document is_page_cache_freeable()

[Johannes Weiner <hannes@cmpxchg.org>]

On Wed, Jul 22, 2009 at 07:50:31PM +0200, Johannes Weiner wrote:
> On Wed, Jul 22, 2009 at 12:49:44PM -0400, Christoph Lameter wrote:
> > >  static inline int is_page_cache_freeable(struct page *page)
> > >  {
> > > -	return page_count(page) - !!page_has_private(page) == 2;
> > > +	return page_count(page) - page_has_private(page) == 2;
> > 
> > That looks funky and in need of comments.

Enlighten the reader of this code about what reference count makes a
page cache page freeable.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/vmscan.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 67e2824..d18f46d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -286,6 +286,11 @@ static inline int page_mapping_inuse(struct page *page)
 
 static inline int is_page_cache_freeable(struct page *page)
 {
+	/*
+	 * A freeable page cache page is referenced only by the caller
+	 * that isolated the page, the page cache itself and
+	 * optionally the page's buffers, if any.
+	 */
 	return page_count(page) - page_has_private(page) == 2;
 }
 
-- 
1.6.3

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