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 16:21, Su Yue wrote:
> 
> 
> 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.

Then fix it.

It's not a normal behavior in this case.

Thanks,
Qu

> 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)
>>>   {
>>>
>>
> 
> 
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