[RFC PATCH V6 09/15] Btrfs: subpagesize-blocksize: __extent_writepage: Write only dirty blocks of a page.

[Chandan Rajendra <chandan@linux.vnet.ibm.com>]

The code now loops across 'ordered extents' instead of 'extent maps' to figure
out the dirty blocks of the page to be submitted for a write operation.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
---
 fs/btrfs/extent_io.c | 74 ++++++++++++++++++++--------------------------------
 1 file changed, 29 insertions(+), 45 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index a3b3d01..37d845d 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3186,18 +3186,18 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
 				 int write_flags, int *nr_ret)
 {
 	struct extent_io_tree *tree = epd->tree;
+	struct btrfs_ordered_extent *ordered;
 	u64 start = page_offset(page);
 	u64 page_end = start + PAGE_CACHE_SIZE - 1;
 	u64 end;
 	u64 cur = start;
 	u64 extent_offset;
-	u64 block_start;
+	u64 extent_end;
 	u64 iosize;
 	sector_t sector;
 	struct extent_state *cached_state = NULL;
-	struct extent_map *em;
 	struct block_device *bdev;
-	size_t pg_offset = 0;
+	size_t pg_offset;
 	size_t blocksize;
 	int ret = 0;
 	int nr = 0;
@@ -3237,59 +3237,46 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
 	blocksize = inode->i_sb->s_blocksize;
 
 	while (cur <= end) {
-		u64 em_end;
 		if (cur >= i_size) {
 			if (tree->ops && tree->ops->writepage_end_io_hook)
 				tree->ops->writepage_end_io_hook(page, cur,
 							 page_end, NULL, 1);
 			break;
 		}
-		em = epd->get_extent(inode, page, pg_offset, cur,
-				     end - cur + 1, 1);
-		if (IS_ERR_OR_NULL(em)) {
-			SetPageError(page);
-			ret = PTR_ERR_OR_ZERO(em);
-			break;
-		}
 
-		extent_offset = cur - em->start;
-		em_end = extent_map_end(em);
-		BUG_ON(em_end <= cur);
+		ordered = btrfs_lookup_ordered_extent(inode, cur);
+		if (!ordered) {
+			cur += blocksize;
+			continue;
+ 		}
+
+		pg_offset = cur & (PAGE_CACHE_SIZE - 1);
+
+		extent_offset = cur - ordered->file_offset;
+		extent_end = ordered->file_offset + ordered->len;
+		extent_end = (extent_end < ordered->file_offset) ? -1 : extent_end;
+		BUG_ON(extent_end <= cur);
 		BUG_ON(end < cur);
-		iosize = min(em_end - cur, end - cur + 1);
+		iosize = min(extent_end - cur, end - cur + 1);
 		iosize = ALIGN(iosize, blocksize);
-		sector = (em->block_start + extent_offset) >> 9;
-		bdev = em->bdev;
-		block_start = em->block_start;
-		compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
-		free_extent_map(em);
-		em = NULL;
+
+		sector = (ordered->start + extent_offset) >> 9;
+		bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
+		compressed = test_bit(BTRFS_ORDERED_COMPRESSED, &ordered->flags);
+		btrfs_put_ordered_extent(ordered);
+		ordered = NULL;
 
 		/*
 		 * compressed and inline extents are written through other
 		 * paths in the FS
 		 */
-		if (compressed || block_start == EXTENT_MAP_HOLE ||
-		    block_start == EXTENT_MAP_INLINE) {
-			/*
-			 * end_io notification does not happen here for
-			 * compressed extents
-			 */
-			if (!compressed && tree->ops &&
-			    tree->ops->writepage_end_io_hook)
-				tree->ops->writepage_end_io_hook(page, cur,
-							 cur + iosize - 1,
-							 NULL, 1);
-			else if (compressed) {
-				/* we don't want to end_page_writeback on
-				 * a compressed extent.  this happens
-				 * elsewhere
-				 */
-				nr++;
-			}
-
+		if (compressed) {
+			/* we don't want to end_page_writeback on
+			 * a compressed extent.  this happens
+			 * elsewhere
+ 			 */
+			nr++;
 			cur += iosize;
-			pg_offset += iosize;
 			continue;
 		}
 
@@ -3320,7 +3307,6 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
 				SetPageError(page);
 		}
 		cur = cur + iosize;
-		pg_offset += iosize;
 		nr++;
 	}
 done:
@@ -3348,7 +3334,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 	u64 page_end = start + PAGE_CACHE_SIZE - 1;
 	int ret;
 	int nr = 0;
-	size_t pg_offset = 0;
+	size_t pg_offset;
 	loff_t i_size = i_size_read(inode);
 	unsigned long end_index = i_size >> PAGE_CACHE_SHIFT;
 	int write_flags;
@@ -3383,8 +3369,6 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 		flush_dcache_page(page);
 	}
 
-	pg_offset = 0;
-
 	set_page_extent_mapped(page);
 
 	ret = writepage_delalloc(inode, page, wbc, epd, start, &nr_written);
-- 
1.8.3.1