On 9.06.20 г. 13:19 ч., fdmanana@xxxxxxxxxx wrote:
> From: Filipe Manana <fdmanana@xxxxxxxx>
>
> When relocating a data block group we group extents from the block group
> into a cluster and when the cluster reaches a certain number of extents
> we do the relocation.
We don't reserve more space because the cluster is guaranteed to contain
contiguous extents, namely in relocate_data_extent we have:
if (cluster->nr > 0 && extent_key->objectid != cluster->end + 1)
{
ret = relocate_file_extent_cluster(inode, cluster);
if (ret)
return ret;
cluster->nr = 0;
}
Cluster->end points to the end offset of the last added extent and the
check above ensures that the one which is currently added is also
contiguous. So relocate_file_extent_cluster is always called with
contiguous range of data extents, which might actually be less than
MAX_EXTENTS.
As a matter of fact this is a rather hard requirement since
prealloc_file_extent_cluster assumes that since when it iterates the
extents in the cluster it does:
if (nr + 1 < cluster->nr)
end = cluster->boundary[nr + 1] - 1 - offset;
else
end = cluster->end - offset;
If those extents weren't contiguous we'd be preallocating more space in
the data reloc inode.
