btrfs: add optimized btrfs_ino() version for 64 bits systems
Currently btrfs_ino() tries to use first the objectid of the inode's location key. This is to avoid truncation of the inode number on 32 bits platforms because the i_ino field of struct inode has the unsigned long type, while the objectid is a 64 bits unsigned type (u64) on every system. This logic was added in commit 33345d01 ("Btrfs: Always use 64bit inode number"). However if we are running on a 64 bits system, we can always directly return the i_ino value from struct inode, which eliminates the need for he special if statement that tests for a location key type of BTRFS_ROOT_ITEM_KEY - in which case i_ino may not have the same value as the objectid in the inode's location objectid, it may have a value of BTRFS_EMPTY_SUBVOL_DIR_OBJECTID, for the case of snapshots of trees with subvolumes/snapshots inside them. So add a special version for 64 bits system that directly returns i_ino of struct inode. This eliminates one branch and reduces the overall code size, since btrfs_ino() is an inline function that is extensively used. Before: $ size fs/btrfs/btrfs.ko text data bss dec hex filename 1617487 189240 29032 1835759 1c02ef fs/btrfs/btrfs.ko After: $ size fs/btrfs/btrfs.ko text data bss dec hex filename 1612028 189180 29032 1830240 1bed60 fs/btrfs/btrfs.ko Signed-off-by: Filipe Manana <fdmanana@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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