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

[Su Yue <suy.fnst@cn.fujitsu.com>]

On 12/20/2017 01:41 PM, Qu Wenruo wrote:
> 
> 
> 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.
> 

Tried to let it happen but BUG_ON with -ENOSPC.
Do you mean do_chunk_alloc() in btrfs_reserve_extent() which is called 
while doing CoW?
In progs, allocation of new chunk during CoW depends @root->ref_cows.
However, @root->ref_cows should be set only if @root is root of a fs
trees.

Thanks,
Su

> 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)
>>   {
>>
>