On 19:56 24/02, David Sterba wrote:

On Mon, Feb 22, 2021 at 07:17:49AM -0600, Goldwyn Rodrigues wrote:

quoted

force_nocow can be calculated by btrfs_inode and does not need to be
passed as an argument.

This simplifies run_delalloc_nocow() call from btrfs_run_delalloc_range()
where should_nocow() checks for BTRFS_INODE_NODATASUM and
BTRFS_INODE_PREALLOC flags or if EXTENT_DEFRAG flags are set.

should_nocow() has been re-arranged so EXTENT_DEFRAG has higher priority
in checks.

Why is that? In the check sequence, test_range_bit is called first but
that's more expensive as it needs to iterate the range.

The test_range() is conditional and short-circuited by
inode->defrag_bytes. So, the worst case scenario would be when
defrag_bytes > 0, and EXTENT_DEFRAG is not set for the range.

I did it for readability, but if you think need_force_cow() is faster, I
am fine with keeping it.

quoted

Signed-off-by: Goldwyn Rodrigues <redacted>
---
 fs/btrfs/inode.c | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4f2f1e932751..2115d8cc6f18 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c

@@ -1516,7 +1516,7 @@ static int fallback_to_cow(struct btrfs_inode *inode, struct page *locked_page,
 static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 				       struct page *locked_page,
 				       const u64 start, const u64 end,
-				       int *page_started, int force,
+				       int *page_started,
 				       unsigned long *nr_written)
 {
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;

@@ -1530,6 +1530,7 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 	u64 ino = btrfs_ino(inode);
 	bool nocow = false;
 	u64 disk_bytenr = 0;
+	bool force = inode->flags & BTRFS_INODE_NODATACOW;
 
 	path = btrfs_alloc_path();
 	if (!path) {

@@ -1863,13 +1864,9 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 	return ret;
 }
 
-static inline int need_force_cow(struct btrfs_inode *inode, u64 start, u64 end)
+static inline bool should_nocow(struct btrfs_inode *inode, u64 start, u64 end)
 {
 
-	if (!(inode->flags & BTRFS_INODE_NODATACOW) &&
-	    !(inode->flags & BTRFS_INODE_PREALLOC))
-		return 0;
-
 	/*
 	 * @defrag_bytes is a hint value, no spinlock held here,
 	 * if is not zero, it means the file is defragging.

@@ -1877,9 +1874,15 @@ static inline int need_force_cow(struct btrfs_inode *inode, u64 start, u64 end)
 	 */
 	if (inode->defrag_bytes &&
 	    test_range_bit(&inode->io_tree, start, end, EXTENT_DEFRAG, 0, NULL))
-		return 1;
+		return false;
 
-	return 0;
+	if (inode->flags & BTRFS_INODE_NODATACOW)
+		return true;
+
+	if (inode->flags & BTRFS_INODE_PREALLOC)
+		return true;

So here it needs to do test_range_bit first, while before the two checks
were fast path.

quoted

+
+	return false;
 }
 
 /*

@@ -1891,17 +1894,12 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct page *locked_page
 		struct writeback_control *wbc)
 {
 	int ret;
-	int force_cow = need_force_cow(inode, start, end);
 	const bool zoned = btrfs_is_zoned(inode->root->fs_info);
 
-	if (inode->flags & BTRFS_INODE_NODATACOW && !force_cow) {
-		ASSERT(!zoned);
-		ret = run_delalloc_nocow(inode, locked_page, start, end,
-					 page_started, 1, nr_written);
-	} else if (inode->flags & BTRFS_INODE_PREALLOC && !force_cow) {
+	if (should_nocow(inode, start, end)) {
 		ASSERT(!zoned);
 		ret = run_delalloc_nocow(inode, locked_page, start, end,
-					 page_started, 0, nr_written);
+					 page_started, nr_written);

Merging the two calls into one branch makes sense so that all the
reasons for 'nocow' are in one helper, so ok.

quoted

 	} else if (!inode_can_compress(inode) ||
 		   !inode_need_compress(inode, start, end)) {
 		if (zoned)
-- 
2.30.1

-- 
Goldwyn