[PATCH 01/15] mm: add invalidatepage_range address space operation

[Lukas Czerner <lczerner@redhat.com>]

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 add new address space operation invalidatepage_range which
allows specifying length of bytes to invalidate, rather than assuming
truncate to the end of the page. It also introduce
block_invalidatepage_range() and do_invalidatepage)range() functions for
exactly the same reason.

The caller does not have to implement both aops (invalidatepage and
invalidatepage_range) and the latter is preferred. The old method will be
used only if invalidatepage_range is not implemented by the caller.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
---
 fs/buffer.c                 |   23 ++++++++++++++++++++++-
 include/linux/buffer_head.h |    2 ++
 include/linux/fs.h          |    2 ++
 include/linux/mm.h          |    2 ++
 mm/truncate.c               |   30 ++++++++++++++++++++++++++----
 5 files changed, 54 insertions(+), 5 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index c7062c8..5937f30 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1457,13 +1457,27 @@ static void discard_buffer(struct buffer_head * bh)
  */
 void block_invalidatepage(struct page *page, unsigned long offset)
 {
+	block_invalidatepage_range(page, offset, PAGE_CACHE_SIZE);
+}
+EXPORT_SYMBOL(block_invalidatepage);
+
+void block_invalidatepage_range(struct page *page, unsigned long offset,
+				unsigned long length)
+{
 	struct buffer_head *head, *bh, *next;
 	unsigned int curr_off = 0;
+	unsigned long stop = length + offset;
 
 	BUG_ON(!PageLocked(page));
 	if (!page_has_buffers(page))
 		goto out;
 
+	/*
+	 * Check for overflow
+	 */
+	if (stop < length)
+		stop = PAGE_CACHE_SIZE;
+
 	head = page_buffers(page);
 	bh = head;
 	do {
@@ -1471,6 +1485,12 @@ void block_invalidatepage(struct page *page, unsigned long offset)
 		next = bh->b_this_page;
 
 		/*
+		 * Are we still fully in range ?
+		 */
+		if (next_off > stop)
+			goto out;
+
+		/*
 		 * is this block fully invalidated?
 		 */
 		if (offset <= curr_off)
@@ -1489,7 +1509,8 @@ void block_invalidatepage(struct page *page, unsigned long offset)
 out:
 	return;
 }
-EXPORT_SYMBOL(block_invalidatepage);
+EXPORT_SYMBOL(block_invalidatepage_range);
+
 
 /*
  * We attach and possibly dirty the buffers atomically wrt
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 458f497..9d55645 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -194,6 +194,8 @@ extern int buffer_heads_over_limit;
  * address_spaces.
  */
 void block_invalidatepage(struct page *page, unsigned long offset);
+void block_invalidatepage_range(struct page *page, unsigned long offset,
+				unsigned long length);
 int block_write_full_page(struct page *page, get_block_t *get_block,
 				struct writeback_control *wbc);
 int block_write_full_page_endio(struct page *page, get_block_t *get_block,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8fabb03..b9eaf0c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -620,6 +620,8 @@ struct address_space_operations {
 	/* Unfortunately this kludge is needed for FIBMAP. Don't use it */
 	sector_t (*bmap)(struct address_space *, sector_t);
 	void (*invalidatepage) (struct page *, unsigned long);
+	void (*invalidatepage_range) (struct page *, unsigned long,
+				      unsigned long);
 	int (*releasepage) (struct page *, gfp_t);
 	void (*freepage)(struct page *);
 	ssize_t (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f9f279c..2db6a29 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -998,6 +998,8 @@ struct page *get_dump_page(unsigned long addr);
 
 extern int try_to_release_page(struct page * page, gfp_t gfp_mask);
 extern void do_invalidatepage(struct page *page, unsigned long offset);
+extern void do_invalidatepage_range(struct page *page, unsigned long offset,
+				    unsigned long length);
 
 int __set_page_dirty_nobuffers(struct page *page);
 int __set_page_dirty_no_writeback(struct page *page);
diff --git a/mm/truncate.c b/mm/truncate.c
index 75801ac..e29e5ea 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -39,14 +39,36 @@
  */
 void do_invalidatepage(struct page *page, unsigned long offset)
 {
+	do_invalidatepage_range(page, offset, PAGE_CACHE_SIZE);
+}
+
+void do_invalidatepage_range(struct page *page, unsigned long offset,
+			     unsigned long length)
+{
+	void (*invalidatepage_range)(struct page *, unsigned long,
+				     unsigned long);
 	void (*invalidatepage)(struct page *, unsigned long);
+
+	/*
+	 * Try invalidatepage_range first
+	 */
+	invalidatepage_range = page->mapping->a_ops->invalidatepage_range;
+	if (invalidatepage_range)
+		(*invalidatepage_range)(page, offset, length);
+
+	/*
+	 * When only invalidatepage is registered length must be
+	 * PAGE_CACHE_SIZE
+	 */
 	invalidatepage = page->mapping->a_ops->invalidatepage;
+	if (invalidatepage) {
+		BUG_ON(length != PAGE_CACHE_SIZE);
+		(*invalidatepage)(page, offset);
+	}
 #ifdef CONFIG_BLOCK
-	if (!invalidatepage)
-		invalidatepage = block_invalidatepage;
+	if (!invalidatepage_range && !invalidatepage)
+		block_invalidatepage_range(page, offset, length);
 #endif
-	if (invalidatepage)
-		(*invalidatepage)(page, offset);
 }
 
 static inline void truncate_partial_page(struct page *page, unsigned partial)
-- 
1.7.7.6