On 2020/7/6 下午2:13, Robbie Ko wrote:
> Does anyone have any suggestions?
I believe David's suggestion on using regular readahead is already good
enough for chunk tree.
Especially since chunk tree is not really the main cause for slow mount.
Thanks,
Qu
>
> robbieko 於 2020/7/1 下午5:29 寫道:
>> From: Robbie Ko <robbieko@xxxxxxxxxxxx>
>>
>> When mounting, we always need to read the whole chunk tree,
>> when there are too many chunk items, most of the time is
>> spent on btrfs_read_chunk_tree, because we only read one
>> leaf at a time.
>>
>> We fix this by adding a new readahead mode READA_FORWARD_FORCE,
>> which reads all the leaves after the key in the node when
>> reading a level 1 node.
>>
>> Signed-off-by: Robbie Ko <robbieko@xxxxxxxxxxxx>
>> ---
>> fs/btrfs/ctree.c | 7 +++++--
>> fs/btrfs/ctree.h | 2 +-
>> fs/btrfs/volumes.c | 1 +
>> 3 files changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
>> index 3a7648bff42c..abb9108e2d7d 100644
>> --- a/fs/btrfs/ctree.c
>> +++ b/fs/btrfs/ctree.c
>> @@ -2194,7 +2194,7 @@ static void reada_for_search(struct
>> btrfs_fs_info *fs_info,
>> if (nr == 0)
>> break;
>> nr--;
>> - } else if (path->reada == READA_FORWARD) {
>> + } else if (path->reada == READA_FORWARD || path->reada ==
>> READA_FORWARD_FORCE) {
>> nr++;
>> if (nr >= nritems)
>> break;
>> @@ -2205,12 +2205,15 @@ static void reada_for_search(struct
>> btrfs_fs_info *fs_info,
>> break;
>> }
>> search = btrfs_node_blockptr(node, nr);
>> - if ((search <= target && target - search <= 65536) ||
>> + if ((path->reada == READA_FORWARD_FORCE) ||
>> + (search <= target && target - search <= 65536) ||
>> (search > target && search - target <= 65536)) {
>> readahead_tree_block(fs_info, search);
>> nread += blocksize;
>> }
>> nscan++;
>> + if (path->reada == READA_FORWARD_FORCE)
>> + continue;
>> if ((nread > 65536 || nscan > 32))
>> break;
>> }
>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>> index d404cce8ae40..808bcbdc9530 100644
>> --- a/fs/btrfs/ctree.h
>> +++ b/fs/btrfs/ctree.h
>> @@ -353,7 +353,7 @@ struct btrfs_node {
>> * The slots array records the index of the item or block pointer
>> * used while walking the tree.
>> */
>> -enum { READA_NONE, READA_BACK, READA_FORWARD };
>> +enum { READA_NONE, READA_BACK, READA_FORWARD, READA_FORWARD_FORCE };
>> struct btrfs_path {
>> struct extent_buffer *nodes[BTRFS_MAX_LEVEL];
>> int slots[BTRFS_MAX_LEVEL];
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index 0d6e785bcb98..78fd65abff69 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -7043,6 +7043,7 @@ int btrfs_read_chunk_tree(struct btrfs_fs_info
>> *fs_info)
>> path = btrfs_alloc_path();
>> if (!path)
>> return -ENOMEM;
>> + path->reada = READA_FORWARD_FORCE;
>> /*
>> * uuid_mutex is needed only if we are mounting a sprout FS
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