On Tue, Jun 9, 2020 at 11:50 AM Nikolay Borisov <nborisov@xxxxxxxx> wrote:
>
>
>
> 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.
Yes, thanks.
I was biased by the gap detection at prealloc_file_extent_cluster()
and missed that, which in this case can't happen.
So lets drop this.
