On 2019/6/19 下午9:39, David Sterba wrote:
> On Wed, Jun 19, 2019 at 09:37:39AM +0800, Qu Wenruo wrote:
>>> struct btrfs_key {
>>> __u64 objectid;
>>> - __u8 type;
>>> __u64 offset;
>>> + __u8 type;
>>> } __attribute__ ((__packed__));
>>
>> And why not remove the packed attribute?
>
> Because of this (stack usage changes):That's expected as long as we're using btrfs_key on stack. But if we're using btrfs_key on stack and follow the packed feature, then adjacent on stack memory is not accessed aligned, which could cause (unobvious) performance drop. If the unaligned memory access is really causing some performance even on stack memory, then I'd say the bump in stack memory usage is acceptable. If not, then the idea of default -Waddress-of-packed-member makes no sense. Thanks, Qu > > do_relocation +8 (304 -> > 312) > btrfs_orphan_cleanup +16 (128 -> > 144) > btrfs_init_new_device -16 (288 -> > 272) > get_subvol_name_from_objectid +8 (136 -> > 144) > log_conflicting_inodes +8 (184 -> > 192) > btrfs_read_chunk_tree +16 (128 -> > 144) > btrfs_recover_relocation +8 (136 -> > 144) > scrub_stripe +16 (536 -> > 552) > btrfs_clone +16 (352 -> > 368) > free_space_next_bitmap +8 (80 -> > 88) > btrfs_find_orphan_roots +16 (112 -> > 128) > find_free_dev_extent_start +8 (160 -> > 168) > btrfs_lookup_extent_info +8 (160 -> > 168) > btrfs_find_item +8 (80 -> > 88) > btrfs_create_pending_block_groups +8 (120 -> > 128) > btrfs_read_block_groups -24 (176 -> > 152) > __remove_from_free_space_tree +8 (120 -> > 128) > check_committed_ref +8 (104 -> > 112) > replay_one_buffer +8 (152 -> > 160) > fixup_inode_link_counts +8 (96 -> > 104) > btrfs_del_csums +8 (192 -> > 200) > btrfs_search_path_in_tree_user +16 (192 -> > 208) > btrfs_lookup_dentry +8 (168 -> > 176) > __add_tree_block +8 (120 -> > 128) > __btrfs_balance +8 (264 -> > 272) > __lookup_free_space_inode +16 (112 -> > 128) > __readahead_hook +16 (168 -> > 184) > btrfs_get_parent +8 (96 -> > 104) > btrfs_run_dev_replace +8 (88 -> > 96) > add_qgroup_item +8 (80 -> > 88) > merge_reloc_root +16 (240 -> > 256) > link_to_fixup_dir +8 (80 -> > 88) > btrfs_insert_orphan_item +8 (64 -> > 72) > btrfs_delete_delayed_items +8 (184 -> > 192) > btrfs_read_qgroup_config +8 (136 -> > 144) > is_extent_unchanged +8 (152 -> > 160) > btrfs_recover_log_trees +24 (192 -> > 216) > btrfs_create_free_space_tree +8 (136 -> > 144) > send_subvol +8 (136 -> > 144) > btrfs_compare_trees +24 (176 -> > 200) > get_first_ref +8 (136 -> > 144) > qgroup_trace_new_subtree_blocks +8 (176 -> > 184) > qgroup_trace_extent_swap +16 (192 -> > 208) > generic_bin_search +8 (160 -> > 168) > replay_one_name +8 (152 -> > 160) > btrfs_print_tree +8 (160 -> > 168) > __create_free_space_inode +8 (112 -> > 120) > copy_items +24 (328 -> > 352) > walk_down_reloc_tree +8 (160 -> > 168) > btrfs_find_next_key +8 (184 -> > 192) > btrfs_del_inode_ref +8 (144 -> > 152) > btrfs_check_node +16 (144 -> > 160) > find_next_devid +8 (88 -> > 96) > btrfs_new_inode +8 (184 -> > 192) > __add_to_free_space_tree +16 (136 -> > 152) > __btrfs_run_delayed_refs +8 (168 -> > 176) > btrfs_qgroup_trace_subtree +8 (224 -> > 232) > btrfs_lookup_csums_range +8 (184 -> > 192) > __btrfs_update_delayed_inode +8 (112 -> > 120) > lookup_inline_extent_backref +8 (184 -> > 192) > find_data_references +8 (152 -> > 160) > replay_dir_deletes +16 (168 -> > 184) > check_leaf +8 (168 -> > 176) > btrfs_ioctl_get_subvol_info +16 (128 -> > 144) > btrfs_insert_inode_ref +8 (152 -> > 160) > btrfs_finish_sprout +8 (152 -> > 160) > build_backref_tree +8 (272 -> > 280) > insert_extent_data_ref +8 (96 -> > 104) > send_clone -24 (160 -> > 136) > insert_tree_block_ref +8 (56 -> > 64) > read_node_slot +8 (88 -> > 96) > btrfs_csum_file_blocks +8 (168 -> > 176) > replace_path +16 (352 -> > 368) > changed_inode +16 (144 -> > 160) > process_all_refs +16 (112 -> > 128) > btrfs_find_root +16 (144 -> > 160) > reada_walk_down +8 (176 -> > 184) > btrfs_insert_xattr_item +8 (136 -> > 144) > maybe_send_hole +8 (152 -> > 160) > btrfs_uuid_scan_kthread +8 (520 -> > 528) > modify_free_space_bitmap +8 (192 -> > 200) > lookup_extent_data_ref +8 (144 -> > 152) > btrfs_run_delayed_refs_for_head +8 (208 -> > 216) > btrfs_search_dir_index_item +8 (112 -> > 120) > btrfs_prev_leaf +16 (88 -> > 104) > may_destroy_subvol +8 (88 -> > 96) > convert_free_space_to_extents +8 (176 -> > 184) > btrfs_quota_enable +8 (128 -> > 136) > remove_block_group_free_space +8 (120 -> > 128) > __btrfs_drop_extents +24 (352 -> > 376) > btrfs_finish_chunk_alloc +16 (192 -> > 208) > log_dir_items +16 (192 -> > 208) > btrfs_log_changed_extents +8 (240 -> > 248) > update_cache_item +8 (112 -> > 120) > extent_from_logical +8 (104 -> > 112) > btrfs_drop_snapshot +8 (176 -> > 184) > btrfs_realloc_node +8 (208 -> > 216) > did_create_dir +8 (88 -> > 96) > add_qgroup_relation_item +8 (80 -> > 88) > find_dir_range +8 (112 -> > 120) > btrfs_verify_level_key +8 (128 -> > 136) > do_walk_down +8 (336 -> > 344) > get_last_extent +8 (88 -> > 96) > add_keyed_refs +8 (168 -> > 176) > read_block_for_search +8 (168 -> > 176) > can_rmdir +8 (120 -> > 128) > btrfs_insert_empty_inode +8 (40 -> > 48) > btrfs_add_root_ref +8 (144 -> > 152) > __btrfs_free_extent +8 (216 -> > 224) > add_all_parents +8 (160 -> > 168) > btrfs_search_path_in_tree +8 (120 -> > 128) > add_new_free_space_info +8 (72 -> > 80) > btrfs_set_inode_index +8 (96 -> > 104) > btrfs_search_forward +8 (128 -> > 136) > insert_balance_item +8 (232 -> > 240) > btrfs_find_one_extref +8 (104 -> > 112) > scrub_raid56_parity +8 (400 -> > 408) > btrfs_real_readdir +8 (192 -> > 200) > btrfs_log_inode_parent +8 (264 -> > 272) > btrfs_listxattr +8 (168 -> > 176) > convert_free_space_to_bitmaps +8 (168 -> > 176) > btrfs_verify_dev_extents +8 (152 -> > 160) > find_next_extent +8 (120 -> > 128) > btrfs_set_item_key_safe +8 (160 -> > 168) > btrfs_mark_extent_written +16 (296 -> > 312) > replay_xattr_deletes +8 (192 -> > 200) > caching_kthread +8 (128 -> > 136) > btrfs_remove_chunk +8 (184 -> > 192) > scrub_print_warning_inode +8 (208 -> > 216) > caching_thread +8 (184 -> > 192) > log_new_dir_dentries +16 (216 -> > 232) > drop_objectid_items +16 (112 -> > 128) > insert_dir_log_key +8 (56 -> > 64) > iterate_dir_item +8 (176 -> > 184) > btrfs_lookup_csum +8 (104 -> > 112) > relocate_tree_blocks +8 (168 -> > 176) > btrfs_build_ref_tree -8 (168 -> > 160) > btrfs_find_highest_objectid +8 (80 -> > 88) > btrfs_insert_dir_item +8 (136 -> > 144) > walk_down_log_tree +8 (176 -> > 184) > btrfs_insert_file_extent +8 (112 -> > 120) > setup_leaf_for_split +8 (120 -> > 128) > btrfs_shrink_device +8 (176 -> > 184) > > LOST (0): > > NEW (544): > btrfs_relocate_sys_chunks > find_first_block_group > add_delayed_refs > process_leaf > > LOST/NEW DELTA: +544 > PRE/POST DELTA: +1840 >
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