linux-kernel - Re: [PATCH 03/11] btrfs: manage heuristic workspace as index 0

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Date:   Thu, 31 Jan 2019 17:10:19 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Dennis Zhou <dennis@...nel.org>
Cc:     David Sterba <dsterba@...e.com>,
        Josef Bacik <josef@...icpanda.com>, Chris Mason <clm@...com>,
        Omar Sandoval <osandov@...ndov.com>,
        Nick Terrell <terrelln@...com>, kernel-team@...com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/11] btrfs: manage heuristic workspace as index 0

On Mon, Jan 28, 2019 at 04:24:29PM -0500, Dennis Zhou wrote:
> While the heuristic workspaces aren't really compression workspaces,
> they use the same interface for managing them. So rather than branching,
> let's just handle them once again as the index 0 compression type.
> 
> Signed-off-by: Dennis Zhou <dennis@...nel.org>
> +const struct btrfs_compress_op btrfs_heuristic_compress = {
> +	.alloc_workspace = alloc_heuristic_ws,
> +	.free_workspace = free_heuristic_ws,
> +};
>  struct workspace_manager {
>  	struct list_head idle_ws;
>  	spinlock_t ws_lock;
> @@ -782,9 +789,8 @@ struct workspace_manager {
>  
>  static struct workspace_manager wsm[BTRFS_COMPRESS_TYPES];

This deserves a comment that the 0th workspace is for the heuristics.

> --- a/fs/btrfs/compression.h
> +++ b/fs/btrfs/compression.h
> @@ -97,7 +97,7 @@ enum btrfs_compression_type {
>  	BTRFS_COMPRESS_ZLIB  = 1,
>  	BTRFS_COMPRESS_LZO   = 2,
>  	BTRFS_COMPRESS_ZSTD  = 3,
> -	BTRFS_COMPRESS_TYPES = 3,
> +	BTRFS_COMPRESS_TYPES = 4,

And here too, as there are only 3 compressors but 4 types as value of
the enum. Or rename BTRFS_COMPRESS_TYPES if you find a better name.

>  };
>  
>  struct btrfs_compress_op {
> @@ -125,6 +125,7 @@ struct btrfs_compress_op {
>  	void (*set_level)(struct list_head *ws, unsigned int type);
>  };
>  
> +extern const struct btrfs_compress_op btrfs_heuristic_compress;
>  extern const struct btrfs_compress_op btrfs_zlib_compress;
>  extern const struct btrfs_compress_op btrfs_lzo_compress;
>  extern const struct btrfs_compress_op btrfs_zstd_compress;
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 9c8e1734429c..20081465a451 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1410,7 +1410,7 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
>  		return -EINVAL;
>  
>  	if (do_compress) {
> -		if (range->compress_type > BTRFS_COMPRESS_TYPES)
> +		if (range->compress_type >= BTRFS_COMPRESS_TYPES)
>  			return -EINVAL;
>  		if (range->compress_type)
>  			compress_type = range->compress_type;
> diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
> index a62e1e837a89..c88e146d8e99 100644
> --- a/fs/btrfs/tree-checker.c
> +++ b/fs/btrfs/tree-checker.c
> @@ -133,9 +133,9 @@ static int check_extent_data_item(struct btrfs_fs_info *fs_info,
>  	 * Support for new compression/encryption must introduce incompat flag,
>  	 * and must be caught in open_ctree().
>  	 */
> -	if (btrfs_file_extent_compression(leaf, fi) > BTRFS_COMPRESS_TYPES) {
> +	if (btrfs_file_extent_compression(leaf, fi) >= BTRFS_COMPRESS_TYPES) {
>  		file_extent_err(fs_info, leaf, slot,
> -	"invalid compression for file extent, have %u expect range [0, %u]",
> +	"invalid compression for file extent, have %u expect range [0, %u)",
>  			btrfs_file_extent_compression(leaf, fi),
>  			BTRFS_COMPRESS_TYPES);

This might become a bit confusing, the message is updated to say [0, 4)
but I'm not sure this is commonly understood that 4 does not belong
there. Either do -1 or define a new enum that contains the maximum
number so BTRFS_COMPRESS_TYPES is not overloaded.