Re: [PATCH v2 05/17] btrfs-progs: lowmem check: introduce modify_block_groups_cache()

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

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On 2017年12月20日 12:57, Su Yue wrote:
> Excluding or pining all metadata blocks is not time-efficient for large
> storage filesystems.
> Here is another way to mark all metadata block groups full and allocate
> a new chunk for CoW. So new reservered extents never overwrite
> extents.
> 
> Introduce modify_block_groups_cache() to modify all blocks groups
> cache state and set all extents in block groups unfree in free space
> cache.
> 
> Suggested-by: Qu Wenruo <wqu@suse.com>
> Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com>
> ---
>  cmds-check.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 83 insertions(+)
> 
> diff --git a/cmds-check.c b/cmds-check.c
> index dd46569f3811..d98d4bda7357 100644
> --- a/cmds-check.c
> +++ b/cmds-check.c
> @@ -10828,6 +10828,89 @@ static void reset_cached_block_groups(struct btrfs_fs_info *fs_info)
>  	}
>  }
>  
> +/*
> + * Mark all extents unfree in the block group. And set @block_group->cached
> + * according to @cache.
> + */
> +static int modify_block_group_cache(struct btrfs_fs_info *fs_info,
> +		    struct btrfs_block_group_cache *block_group, int cache)
> +{
> +	struct extent_io_tree *free_space_cache = &fs_info->free_space_cache;
> +	u64 start = block_group->key.objectid;
> +	u64 end = start + block_group->key.offset;
> +
> +	if (cache && !block_group->cached) {
> +		block_group->cached = 1;
> +		clear_extent_dirty(free_space_cache, start, end - 1);
> +	}
> +
> +	if (!cache && block_group->cached) {
> +		block_group->cached = 0;
> +		clear_extent_dirty(free_space_cache, start, end - 1);
> +	}
> +	return 0;
> +}
> +
> +/*
> + * Modify block groups which have @flags unfree in free space cache.
> + *
> + * @cache: if 0, clear block groups cache state;
> + *         not 0, mark blocks groups cached.

The naming of the function and the @cache parameter is quite confusing.

And so is the later usage of the function.
It's used by both marking all block groups full and revert the full mark
as cleanup.


I would call the function mark_block_groups_full() to do the full
marking thing, without the extra @cache parameter.

And another function to clear_block_groups_full() to make them into back
to normal status.

Thanks,
Qu
> + */
> +static int modify_block_groups_cache(struct btrfs_fs_info *fs_info, u64 flags,
> +				     int cache)
> +{
> +	struct btrfs_root *root = fs_info->extent_root;
> +	struct btrfs_key key;
> +	struct btrfs_path path;
> +	struct btrfs_block_group_cache *bg_cache;
> +	struct btrfs_block_group_item *bi;
> +	struct btrfs_block_group_item bg_item;
> +	struct extent_buffer *eb;
> +	int slot;
> +	int ret;
> +
> +	key.objectid = 0;
> +	key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
> +	key.offset = 0;
> +
> +	btrfs_init_path(&path);
> +	ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
> +	if (ret < 0) {
> +		error("fail to search block groups due to %s", strerror(-ret));
> +		goto out;
> +	}
> +
> +	while (1) {
> +		eb = path.nodes[0];
> +		slot = path.slots[0];
> +		btrfs_item_key_to_cpu(eb, &key, slot);
> +		bg_cache = btrfs_lookup_block_group(fs_info, key.objectid);
> +		if (!bg_cache) {
> +			ret = -ENOENT;
> +			goto out;
> +		}
> +
> +		bi = btrfs_item_ptr(eb, slot, struct btrfs_block_group_item);
> +		read_extent_buffer(eb, &bg_item, (unsigned long)bi,
> +				   sizeof(bg_item));
> +		if (btrfs_block_group_flags(&bg_item) & flags)
> +			modify_block_group_cache(fs_info, bg_cache, cache);
> +
> +		ret = btrfs_next_item(root, &path);
> +		if (ret > 0) {
> +			ret = 0;
> +			goto out;
> +		}
> +		if (ret < 0)
> +			goto out;
> +	}
> +
> +out:
> +	btrfs_release_path(&path);
> +	return ret;
> +}
> +
>  static int check_extent_refs(struct btrfs_root *root,
>  			     struct cache_tree *extent_cache)
>  {
> 


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