Re: [PATCH v2] Btrfs: setup free ino caching in a more asynchronous way

[Arne Jansen <sensille@gmx.net>]

On 26.05.2011 08:38, Li Zefan wrote:
> For a filesystem that has lots of files in it, the first time we mount
> it with free ino caching support, it can take quite a long time to
> setup the caching before we can create new files.
> 
> Here we fill the cache with [highest_ino, BTRFS_LAST_FREE_OBJECTID]
> before we start the caching thread to search through the extent tree.

This also sound like a very good consumer for the readahead-API.

-Arne

> 
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
> 
> based on the integration-test branch.
> 
> v2: fixed an off-by-one bug
> 
> ---
>  fs/btrfs/inode-map.c |   28 ++++++++++++++++++++++------
>  1 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c
> index 0009705..3262cd1 100644
> --- a/fs/btrfs/inode-map.c
> +++ b/fs/btrfs/inode-map.c
> @@ -60,12 +60,12 @@ again:
>  
>  	while (1) {
>  		smp_mb();
> -		if (fs_info->closing > 1)
> +		if (fs_info->closing)
>  			goto out;
>  
>  		leaf = path->nodes[0];
>  		slot = path->slots[0];
> -		if (path->slots[0] >= btrfs_header_nritems(leaf)) {
> +		if (slot >= btrfs_header_nritems(leaf)) {
>  			ret = btrfs_next_leaf(root, path);
>  			if (ret < 0)
>  				goto out;
> @@ -100,7 +100,7 @@ again:
>  		if (key.type != BTRFS_INODE_ITEM_KEY)
>  			goto next;
>  
> -		if (key.objectid >= BTRFS_LAST_FREE_OBJECTID)
> +		if (key.objectid >= root->highest_objectid)
>  			break;
>  
>  		if (last != (u64)-1 && last + 1 != key.objectid) {
> @@ -114,9 +114,9 @@ next:
>  		path->slots[0]++;
>  	}
>  
> -	if (last < BTRFS_LAST_FREE_OBJECTID - 1) {
> +	if (last < root->highest_objectid - 1) {
>  		__btrfs_add_free_space(ctl, last + 1,
> -				       BTRFS_LAST_FREE_OBJECTID - last - 1);
> +				       root->highest_objectid - last - 1);
>  	}
>  
>  	spin_lock(&root->cache_lock);
> @@ -136,8 +136,10 @@ out:
>  
>  static void start_caching(struct btrfs_root *root)
>  {
> +	struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
>  	struct task_struct *tsk;
>  	int ret;
> +	u64 objectid;
>  
>  	spin_lock(&root->cache_lock);
>  	if (root->cached != BTRFS_CACHE_NO) {
> @@ -156,6 +158,19 @@ static void start_caching(struct btrfs_root *root)
>  		return;
>  	}
>  
> +	/*
> +	 * It can be quite time-consuming to fill the cache by searching
> +	 * through the extent tree, and this can keep ino allocation path
> +	 * waiting. Therefore at start we quickly find out the highest
> +	 * inode number and we know we can use inode numbers which fall in
> +	 * [highest_ino + 1, BTRFS_LAST_FREE_OBJECTID].
> +	 */
> +	ret = btrfs_find_free_objectid(root, &objectid);
> +	if (!ret && objectid <= BTRFS_LAST_FREE_OBJECTID) {
> +		__btrfs_add_free_space(ctl, objectid,
> +				       BTRFS_LAST_FREE_OBJECTID - objectid + 1);
> +	}
> +
>  	tsk = kthread_run(caching_kthread, root, "btrfs-ino-cache-%llu\n",
>  			  root->root_key.objectid);
>  	BUG_ON(IS_ERR(tsk));
> @@ -209,7 +224,8 @@ again:
>  
>  		start_caching(root);
>  
> -		if (objectid <= root->cache_progress)
> +		if (objectid <= root->cache_progress ||
> +		    objectid > root->highest_objectid)
>  			__btrfs_add_free_space(ctl, objectid, 1);
>  		else
>  			__btrfs_add_free_space(pinned, objectid, 1);