[PATCH] Btrfs: make should_defrag_range() understood compressed extents

[Timofey Titovets <nefelim4ag@gmail.com>]

Both, defrag ioctl and autodefrag - call btrfs_defrag_file()
for file defragmentation.

Kernel target extent size default is 256KiB
Btrfs progs by default, use 32MiB.

Both bigger then max (not fragmented) compressed extent size 128KiB.
That lead to rewrite all compressed data on disk.

Fix that and also make should_defrag_range() understood
if requested target compression are same as current extent compression type.
To avoid useless recompression of compressed extents.

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
---
 fs/btrfs/ioctl.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index be5bd81b3669..12d4fa5d6dec 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1008,7 +1008,7 @@ static bool defrag_check_next_extent(struct inode *inode, struct extent_map *em)
 
 static int should_defrag_range(struct inode *inode, u64 start, u32 thresh,
 			       u64 *last_len, u64 *skip, u64 *defrag_end,
-			       int compress)
+			       int compress, int compress_type)
 {
 	struct extent_map *em;
 	int ret = 1;
@@ -1043,8 +1043,29 @@ static int should_defrag_range(struct inode *inode, u64 start, u32 thresh,
 	 * real extent, don't bother defragging it
 	 */
 	if (!compress && (*last_len == 0 || *last_len >= thresh) &&
-	    (em->len >= thresh || (!next_mergeable && !prev_mergeable)))
+	    (em->len >= thresh || (!next_mergeable && !prev_mergeable))) {
 		ret = 0;
+		goto out;
+	}
+
+
+	/*
+	 * Try not recompress compressed extents
+	 * thresh >= BTRFS_MAX_UNCOMPRESSED will lead to
+	 * recompress all compressed extents
+	 */
+	if (em->compress_type != 0 && thresh >= BTRFS_MAX_UNCOMPRESSED) {
+		if (!compress) {
+			if (em->len == BTRFS_MAX_UNCOMPRESSED)
+				ret = 0;
+		} else {
+			if (em->compress_type != compress_type)
+				goto out;
+			if (em->len == BTRFS_MAX_UNCOMPRESSED)
+				ret = 0;
+		}
+	}
+
 out:
 	/*
 	 * last_len ends up being a counter of how many bytes we've defragged.
@@ -1342,7 +1363,8 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
 
 		if (!should_defrag_range(inode, (u64)i << PAGE_SHIFT,
 					 extent_thresh, &last_len, &skip,
-					 &defrag_end, do_compress)){
+					 &defrag_end, do_compress,
+					 compress_type)){
 			unsigned long next;
 			/*
 			 * the should_defrag function tells us how much to skip
-- 
2.15.1