From 3532cb3306d08409c0b42bdcf9ad9d59f2893bb0 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Tue, 5 Nov 2024 11:56:45 +0000 Subject: [PATCH] btrfs: remove hole from struct btrfs_delayed_node On x86_64 and a release kernel, there's a 4 bytes hole in the structure after the ref count field: struct btrfs_delayed_node { u64 inode_id; /* 0 8 */ u64 bytes_reserved; /* 8 8 */ struct btrfs_root * root; /* 16 8 */ struct list_head n_list; /* 24 16 */ struct list_head p_list; /* 40 16 */ struct rb_root_cached ins_root; /* 56 16 */ /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */ struct rb_root_cached del_root; /* 72 16 */ struct mutex mutex; /* 88 32 */ struct btrfs_inode_item inode_item; /* 120 160 */ /* --- cacheline 4 boundary (256 bytes) was 24 bytes ago --- */ refcount_t refs; /* 280 4 */ /* XXX 4 bytes hole, try to pack */ u64 index_cnt; /* 288 8 */ long unsigned int flags; /* 296 8 */ int count; /* 304 4 */ u32 curr_index_batch_size; /* 308 4 */ u32 index_item_leaves; /* 312 4 */ /* size: 320, cachelines: 5, members: 15 */ /* sum members: 312, holes: 1, sum holes: 4 */ /* padding: 4 */ }; Move the 'count' field, which is 4 bytes long, to just below the ref count field, so we eliminate the hole and reduce the structure size from 320 bytes down to 312 bytes: struct btrfs_delayed_node { u64 inode_id; /* 0 8 */ u64 bytes_reserved; /* 8 8 */ struct btrfs_root * root; /* 16 8 */ struct list_head n_list; /* 24 16 */ struct list_head p_list; /* 40 16 */ struct rb_root_cached ins_root; /* 56 16 */ /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */ struct rb_root_cached del_root; /* 72 16 */ struct mutex mutex; /* 88 32 */ struct btrfs_inode_item inode_item; /* 120 160 */ /* --- cacheline 4 boundary (256 bytes) was 24 bytes ago --- */ refcount_t refs; /* 280 4 */ int count; /* 284 4 */ u64 index_cnt; /* 288 8 */ long unsigned int flags; /* 296 8 */ u32 curr_index_batch_size; /* 304 4 */ u32 index_item_leaves; /* 308 4 */ /* size: 312, cachelines: 5, members: 15 */ /* last cacheline: 56 bytes */ }; This now allows to have 13 delayed nodes per 4K page instead of 12. Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/delayed-inode.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/delayed-inode.h b/fs/btrfs/delayed-inode.h index 7cfefdfe54ea67..f4d9feac0d0ea7 100644 --- a/fs/btrfs/delayed-inode.h +++ b/fs/btrfs/delayed-inode.h @@ -64,9 +64,9 @@ struct btrfs_delayed_node { struct mutex mutex; struct btrfs_inode_item inode_item; refcount_t refs; + int count; u64 index_cnt; unsigned long flags; - int count; /* * The size of the next batch of dir index items to insert (if this * node is from a directory inode). Protected by @mutex.