svn commit: r242520 - head/sys/ufs/ffs

[Bruce Evans]

On Sat, 3 Nov 2012, Kirk McKusick wrote:

> Log:
>  When a file is first being written, the dynamic block reallocation
>  (implemented by ffs_reallocblks_ufs[12]) relocates the file's blocks
>  so as to cluster them together into a contiguous set of blocks on
>  the disk.
>
>  When the cluster crosses the boundary into the first indirect block,
>  the first indirect block is initially allocated in a position
>  immediately following the last direct block.  Block reallocation
>  would usually destroy locality by moving the indirect block out of
>  the way to keep the data blocks contiguous.  This change compensates
>  for this problem by noting that the first indirect block should be
>  left immediately following the last direct block.  It then tries
>  to start a new cluster of contiguous blocks (referenced by the
>  indirect block) immediately following the indirect block.
>
>  We should also do this for other indirect block boundaries, but it
>  is only important for the first one.
>
>  Suggested by: Bruce Evans
>  MFC:          2 weeks

Thanks.  Sorry I haven't got around to testing your version of this.

Bruce