On 2019/3/19 下午3:04, Nikolay Borisov wrote:
>
>
> On 19.03.19 г. 8:04 ч., Qu Wenruo wrote:
>> This new tree block flag is to indicate the tree block belongs to a log
>> tree.
>>
>> For btrfs on-disk format, there are several different trees could use
>> the same owner number:
>> - ordinary subvolume tree
>> - log tree for ordinary subvolume
>> - reloc tree for ordinary subvolume
>>
>> It's possible to do the backref walk or use the content to determine the
>> real owner of the tree block.
>> But backref walk is too expensive, content detection is not reliable.
>>
>> So adding a new flag to explicitly show the owner of log tree.
>>
>> Thankfully, tree-checker hasn't checked header flags yet, and there is
>> no real user for this flag yet.
>> So we don't need to introduce any compatibility flag for this
>> modification.
>>
>> The introduction of this new flag makes tree block owner easier to
>> distinguish, making life easier for:
>> - tree checker on log tree
>> Log tree could contain some items impossible for regular trees
>> - performance profiler
>> Now it's much easier to distinguish log tree.
>>
>> Signed-off-by: Qu Wenruo <w...@suse.com>
>> ---
>> fs/btrfs/disk-io.c | 1 +
>> include/uapi/linux/btrfs_tree.h | 6 ++++++
>> 2 files changed, 7 insertions(+)
>>
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index 6fe9197f6ee4..8cffdb7789d8 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -1362,6 +1362,7 @@ static struct btrfs_root *alloc_log_tree(struct
>> btrfs_trans_handle *trans,
>> return ERR_CAST(leaf);
>> }
>>
>> + btrfs_set_header_flag(leaf, BTRFS_HEADER_FLAG_LOG);
>> root->node = leaf;
>
> Unless you are going to tag ALL extent buffers which are allocated as
> part of the log tree this patch is redundant, because even now you can
> detect the root of the log tree by simply checking for the
> root->root_key.objectid.
That is obvious.
As mentioned, the purpose is to detect owner for root->log_root.
So it's to tag all log tree blocks.
> Alternatively if you are going to be tagging
> all such blocks then those 2 patches need to be part of a larger series
> so the intended usage is more clear.
The problem is, the larger part is not going to be a kernel patch.
Mostly btrfs-progs patch and 3rd-part kernel profiling tool.
>
>>
>> btrfs_mark_buffer_dirty(root->node);
>> diff --git a/include/uapi/linux/btrfs_tree.h
>> b/include/uapi/linux/btrfs_tree.h
>> index e974f4bb5378..d4ef80b702a0 100644
>> --- a/include/uapi/linux/btrfs_tree.h
>> +++ b/include/uapi/linux/btrfs_tree.h
>> @@ -447,9 +447,15 @@ struct btrfs_free_space_header {
>> __le64 num_bitmaps;
>> } __attribute__ ((__packed__));
>>
>> +/* Tree/super has written to disk */
> tree block has been correctly written to disk
The trick here is, super block reuses this flag.
So we still need to mention the super block part.
Thanks,
Qu
>
>> #define BTRFS_HEADER_FLAG_WRITTEN (1ULL << 0)
>> +
>> +/* Tree block which gets relocated */
>
> tree block belongs to a relocation tree
>
>> #define BTRFS_HEADER_FLAG_RELOC (1ULL << 1)
>>
>> +/* Tree block which belows to log tree */
>> +#define BTRFS_HEADER_FLAG_LOG (1ULL << 2)
>> +
>> /* Super block flags */
>> /* Errors detected */
>> #define BTRFS_SUPER_FLAG_ERROR (1ULL << 2)
>>
