Re: [PATCH v2 06/17] btrfs-progs: lowmem check: introduce force_cow_in_new_chunk()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2017年12月20日 12:57, Su Yue wrote:
> Introduce create_chunk_and_block_block_group() to allocate new chunk
> and corresponding block group.
> 
> The new function force_cow_in_new_chunk() first allocates new chunk
> and records its start.
> Then it modifies all metadata block groups cached and full.
> Finally it marks the new block group uncached and unfree.
> In the next CoW, extents states will be updated automatically by
> cache_block_group().
> 
> Suggested-by: Qu Wenruo <wqu@suse.com>
> Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com>
> ---
>  cmds-check.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 80 insertions(+)
> 
> diff --git a/cmds-check.c b/cmds-check.c
> index d98d4bda7357..311c8a9f45e8 100644
> --- a/cmds-check.c
> +++ b/cmds-check.c
> @@ -10911,6 +10911,86 @@ out:
>  	return ret;
>  }
>  
> +static int create_chunk_and_block_group(struct btrfs_fs_info *fs_info,
> +					u64 flags, u64 *start, u64 *nbytes)
> +{
> +	struct btrfs_trans_handle *trans;
> +	struct btrfs_root *root = fs_info->extent_root;
> +	int ret;
> +
> +	if ((flags & BTRFS_BLOCK_GROUP_TYPE_MASK) == 0)
> +		return -EINVAL;
> +
> +	trans = btrfs_start_transaction(root, 1);
> +	if (IS_ERR(trans)) {
> +		ret = PTR_ERR(trans);
> +		error("error starting transaction %s", strerror(-ret));
> +		return ret;
> +	}
> +	ret = btrfs_alloc_chunk(trans, fs_info, start, nbytes, flags);
> +	if (ret) {
> +		error("fail to allocate new chunk %s", strerror(-ret));
> +		goto out;
> +	}
> +	ret = btrfs_make_block_group(trans, fs_info, 0, flags,
> +			     BTRFS_FIRST_CHUNK_TREE_OBJECTID, *start, *nbytes);
> +	if (ret) {
> +		error("fail to make block group for chunk %llu %llu %s",
> +		      *start, *nbytes, strerror(-ret));
> +		goto out;
> +	}
> +out:
> +	btrfs_commit_transaction(trans, root);
> +	return ret;
> +}
> +
> +static int force_cow_in_new_chunk(struct btrfs_fs_info *fs_info)
> +{
> +	struct btrfs_block_group_cache *bg;
> +	u64 start;
> +	u64 nbytes;
> +	u64 alloc_profile;
> +	u64 flags;
> +	int ret;
> +
> +	alloc_profile = (fs_info->avail_metadata_alloc_bits &
> +			 fs_info->metadata_alloc_profile);
> +	flags = BTRFS_BLOCK_GROUP_METADATA | alloc_profile;
> +	if (btrfs_fs_incompat(fs_info, MIXED_GROUPS))
> +		flags |= BTRFS_BLOCK_GROUP_DATA;
> +
> +	ret = create_chunk_and_block_group(fs_info, flags, &start, &nbytes);

Why bother allocating a new chunk by yourself?

Just mark all block groups full and that's all.

Any later tree block allocation like btrfs_search_slot() with @cow = 1
will trigger chunk allocation automatically.

Thanks,
Qu

> +	if (!ret)
> +		printf("Create new chunk %llu %llu\n", start, nbytes);
> +	else
> +		goto err;
> +
> +	flags = BTRFS_BLOCK_GROUP_METADATA;
> +	/* Mark all metadata block groups cached and full in free space*/
> +	ret = modify_block_groups_cache(fs_info, flags, 1);
> +	if (ret)
> +		goto clear_bg_cache;
> +
> +	bg = btrfs_lookup_block_group(fs_info, start);
> +	if (!bg) {
> +		ret = -ENOENT;
> +		error("fail to look up block group %llu %llu", start, nbytes);
> +		goto clear_bg_cache;
> +	}
> +
> +	/* Clear block group cache just allocated */
> +	ret = modify_block_group_cache(fs_info, bg, 0);
> +	if (ret)
> +		goto clear_bg_cache;
> +
> +	return 0;
> +
> +clear_bg_cache:
> +	modify_block_groups_cache(fs_info, flags, 0);
> +err:
> +	return ret;
> +}
> +
>  static int check_extent_refs(struct btrfs_root *root,
>  			     struct cache_tree *extent_cache)
>  {
> 


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