btrfs: cleanup the COW fallback logic in run_delalloc_nocow

Use the block group pointer used to track the outstanding NOCOW writes as
a boolean to remove the duplicate nocow variable, and keep it contained
in the main loop to simplify the logic.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 0d973a9..1fb1e4a 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1974,8 +1974,6 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
        int ret;
        bool check_prev = true;
        u64 ino = btrfs_ino(inode);
-       struct btrfs_block_group *bg;
-       bool nocow = false;
        struct can_nocow_file_extent_args nocow_args = { 0 };
 
        path = btrfs_alloc_path();
@@ -1993,6 +1991,7 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
        nocow_args.writeback_path = true;
 
        while (1) {
+               struct btrfs_block_group *nocow_bg = NULL;
                struct btrfs_ordered_extent *ordered;
                struct btrfs_key found_key;
                struct btrfs_file_extent_item *fi;
@@ -2003,8 +2002,6 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
                int extent_type;
                bool is_prealloc;
 
-               nocow = false;
-
                ret = btrfs_lookup_file_extent(NULL, root, path, ino,
                                               cur_offset, 0);
                if (ret < 0)
@@ -2063,7 +2060,7 @@ next_slot:
                if (found_key.offset > cur_offset) {
                        extent_end = found_key.offset;
                        extent_type = 0;
-                       goto out_check;
+                       goto must_cow;
                }
 
                /*
@@ -2096,18 +2093,19 @@ next_slot:
                if (ret < 0)
                        goto error;
                if (ret == 0)
-                       goto out_check;
+                       goto must_cow;
 
                ret = 0;
-               bg = btrfs_inc_nocow_writers(fs_info, nocow_args.disk_bytenr);
-               if (bg)
-                       nocow = true;
-out_check:
-               /*
-                * If nocow is false then record the beginning of the range
-                * that needs to be COWed
-                */
-               if (!nocow) {
+               nocow_bg = btrfs_inc_nocow_writers(fs_info, nocow_args.disk_bytenr);
+               if (!nocow_bg) {
+must_cow:
+                       /*
+                        * If we can't perform NOCOW writeback for the range,
+                        * then record the beginning of the range that needs to
+                        * be COWed.  It will be written out before the next
+                        * NOCOW range if we find one, or when exiting this
+                        * loop.
+                        */
                        if (cow_start == (u64)-1)
                                cow_start = cur_offset;
                        cur_offset = extent_end;
@@ -2128,8 +2126,10 @@ out_check:
                        ret = fallback_to_cow(inode, locked_page,
                                              cow_start, found_key.offset - 1);
                        cow_start = (u64)-1;
-                       if (ret)
+                       if (ret) {
+                               btrfs_dec_nocow_writers(nocow_bg);
                                goto error;
+                       }
                }
 
                nocow_end = cur_offset + nocow_args.num_bytes - 1;
@@ -2146,6 +2146,7 @@ out_check:
                                          ram_bytes, BTRFS_COMPRESS_NONE,
                                          BTRFS_ORDERED_PREALLOC);
                        if (IS_ERR(em)) {
+                               btrfs_dec_nocow_writers(nocow_bg);
                                ret = PTR_ERR(em);
                                goto error;
                        }
@@ -2159,6 +2160,7 @@ out_check:
                                ? (1 << BTRFS_ORDERED_PREALLOC)
                                : (1 << BTRFS_ORDERED_NOCOW),
                                BTRFS_COMPRESS_NONE);
+               btrfs_dec_nocow_writers(nocow_bg);
                if (IS_ERR(ordered)) {
                        if (is_prealloc) {
                                btrfs_drop_extent_map_range(inode, cur_offset,
@@ -2168,11 +2170,6 @@ out_check:
                        goto error;
                }
 
-               if (nocow) {
-                       btrfs_dec_nocow_writers(bg);
-                       nocow = false;
-               }
-
                if (btrfs_is_data_reloc_root(root))
                        /*
                         * Error handled later, as we must prevent
@@ -2213,10 +2210,10 @@ out_check:
                        goto error;
        }
 
-error:
-       if (nocow)
-               btrfs_dec_nocow_writers(bg);
+       btrfs_free_path(path);
+       return 0;
 
+error:
        /*
         * If an error happened while a COW region is outstanding, cur_offset
         * needs to be reset to cow_start to ensure the COW region is unlocked
@@ -2224,7 +2221,7 @@ error:
         */
        if (cow_start != (u64)-1)
                cur_offset = cow_start;
-       if (ret && cur_offset < end)
+       if (cur_offset < end)
                extent_clear_unlock_delalloc(inode, cur_offset, end,
                                             locked_page, EXTENT_LOCKED |
                                             EXTENT_DELALLOC | EXTENT_DEFRAG |