mm: change invalidatepage prototype to accept length

Currently there is no way to truncate partial page where the end
truncate point is not at the end of the page. This is because it was not
needed and the functionality was enough for file system truncate
operation to work properly. However more file systems now support punch
hole feature and it can benefit from mm supporting truncating page just
up to the certain point.

Specifically, with this functionality truncate_inode_pages_range() can
be changed so it supports truncating partial page at the end of the
range (currently it will BUG_ON() if 'end' is not at the end of the
page).

This commit changes the invalidatepage() address space operation
prototype to accept range to be invalidated and update all the instances
for it.

We also change the block_invalidatepage() in the same way and actually
make a use of the new length argument implementing range invalidation.

Actual file system implementations will follow except the file systems
where the changes are really simple and should not change the behaviour
in any way .Implementation for truncate_page_range() which will be able
to accept page unaligned ranges will follow as well.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>

2 files changed, 10 insertions, 7 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index daed28dd583..829a77c6283 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -48,7 +48,7 @@ static void read_cache_pages_invalidate_page(struct address_space *mapping,
 		if (!trylock_page(page))
 			BUG();
 		page->mapping = mapping;
-		do_invalidatepage(page, 0);
+		do_invalidatepage(page, 0, PAGE_CACHE_SIZE);
 		page->mapping = NULL;
 		unlock_page(page);
 	}
diff --git a/mm/truncate.c b/mm/truncate.c
index c75b736e54b..fdba083f0d7 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -26,7 +26,8 @@
 /**
  * do_invalidatepage - invalidate part or all of a page
  * @page: the page which is affected
- * @offset: the index of the truncation point
+ * @offset: start of the range to invalidate
+ * @length: length of the range to invalidate
  *
  * do_invalidatepage() is called when all or part of the page has become
  * invalidated by a truncate operation.
@@ -37,16 +38,18 @@
  * point.  Because the caller is about to free (and possibly reuse) those
  * blocks on-disk.
  */
-void do_invalidatepage(struct page *page, unsigned long offset)
+void do_invalidatepage(struct page *page, unsigned int offset,
+		       unsigned int length)
 {
-	void (*invalidatepage)(struct page *, unsigned long);
+	void (*invalidatepage)(struct page *, unsigned int, unsigned int);
+
 	invalidatepage = page->mapping->a_ops->invalidatepage;
 #ifdef CONFIG_BLOCK
 	if (!invalidatepage)
 		invalidatepage = block_invalidatepage;
 #endif
 	if (invalidatepage)
-		(*invalidatepage)(page, offset);
+		(*invalidatepage)(page, offset, length);
 }
 
 static inline void truncate_partial_page(struct page *page, unsigned partial)
@@ -54,7 +57,7 @@ static inline void truncate_partial_page(struct page *page, unsigned partial)
 	zero_user_segment(page, partial, PAGE_CACHE_SIZE);
 	cleancache_invalidate_page(page->mapping, page);
 	if (page_has_private(page))
-		do_invalidatepage(page, partial);
+		do_invalidatepage(page, partial, PAGE_CACHE_SIZE - partial);
 }
 
 /*
@@ -103,7 +106,7 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
 		return -EIO;
 
 	if (page_has_private(page))
-		do_invalidatepage(page, 0);
+		do_invalidatepage(page, 0, PAGE_CACHE_SIZE);
 
 	cancel_dirty_page(page, PAGE_CACHE_SIZE);