btrfs: reorder btrfs_bio for better packing
After changes in commit 917f32a2 ("btrfs: give struct btrfs_bio a real end_io handler") the layout of btrfs_bio can be improved. There are two holes and the structure size is 264 bytes on release build. By reordering the iterator we can get rid of the holes and the size is 256 bytes which fits to slabs much better. Final layout: struct btrfs_bio { unsigned int mirror_num; /* 0 4 */ struct bvec_iter iter; /* 4 20 */ u64 file_offset; /* 24 8 */ struct btrfs_device * device; /* 32 8 */ u8 * csum; /* 40 8 */ u8 csum_inline[64]; /* 48 64 */ /* --- cacheline 1 boundary (64 bytes) was 48 bytes ago --- */ btrfs_bio_end_io_t end_io; /* 112 8 */ void * private; /* 120 8 */ /* --- cacheline 2 boundary (128 bytes) --- */ struct work_struct end_io_work; /* 128 32 */ struct bio bio; /* 160 96 */ /* size: 256, cachelines: 4, members: 10 */ }; Fixes: 917f32a2 ("btrfs: give struct btrfs_bio a real end_io handler") Signed-off-by: David Sterba <dsterba@suse.com>
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