btrfs: change max_inline default to 2048

The current practical default is ~4k on x86_64 (the logic is more complex,
simplified for brevity), the inlined files land in the metadata group and
thus consume space that could be needed for the real metadata.

The inlining brings some usability surprises:

1) total space consumption measured on various filesystems and btrfs
   with DUP metadata was quite visible because of the duplicated data
   within metadata

2) inlined data may exhaust the metadata, which are more precious in case
   the entire device space is allocated to chunks (ie. balance cannot
   make the space more compact)

3) performance suffers a bit as the inlined blocks are duplicate and
   stored far away on the device.

Proposed fix: set the default to 2048

This fixes namely 1), the total filesysystem space consumption will be on
par with other filesystems.

Partially fixes 2), more data are pushed to the data block groups.

The characteristics of 3) are based on actual small file size
distribution.

The change is independent of the metadata blockgroup type (though it's
most visible with DUP) or system page size as these parameters are not
trival to find out, compared to file size.

Signed-off-by: David Sterba <dsterba@suse.com>
(cherry picked from commit f7e98a7fff8634ae655c666dc2c9fc55a48d0a73)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2cd7267e6ae51952ab9ee7611118ef1528652d12..5fda76675f956eb26f98bc94cdbbf62990d18caa 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2187,7 +2187,7 @@ struct btrfs_ioctl_defrag_range_args {
 #define BTRFS_MOUNT_FRAGMENT_METADATA  (1 << 25)
 
 #define BTRFS_DEFAULT_COMMIT_INTERVAL  (30)
-#define BTRFS_DEFAULT_MAX_INLINE       (8192)
+#define BTRFS_DEFAULT_MAX_INLINE       (2048)
 
 #define btrfs_clear_opt(o, opt)                ((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)          ((o) |= BTRFS_MOUNT_##opt)