On 2020/7/1 下午5:24, robbieko wrote:
> 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.
Well, under most case it would be btrfs_read_block_groups(), unless all
data chunks are very compact with just several large data extents.
>
> 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;
Why not just use regular forward readahead?
Mind to share the reason here? Just to force reada for all tree leaves?
Thanks,
Qu
>
> /*
> * uuid_mutex is needed only if we are mounting a sprout FS
>
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