Enhance the sequential access heuristic used to perform readahead in the

NFS server and reuse it for writes as well to allow writes to the backing
store to be clustered.
- Use a prime number for the size of the heuristic table (1017 is not
  prime).
- Move the logic to locate a heuristic entry from the table and compute
  the sequential count out of VOP_READ() and into a separate routine.
- Use the logic from sequential_heuristic() in vfs_vnops.c to update the
  seqcount when a sequential access is performed rather than just
  increasing seqcount by 1.  This lets the clustering count ramp up
  faster.
- Allow for some reordering of RPCs and if it is detected leave the current
  seqcount as-is rather than dropping back to a seqcount of 1.  Also,
  when out of order access is encountered, cut seqcount in half rather than
  dropping it all the way back to 1 to further aid with reordering.
- Fix the new NFS server to properly update the next offset after a
  successful VOP_READ() so that the readahead actually works.

Some of these changes came from an earlier patch by Bjorn Gronwall that was
forwarded to me by bde@.

Discussed with:	bde, rmacklem, fs@
Submitted by:	Bjorn Gronwall (1, 4)
MFC after:	2 weeks

0 files changed, 0 insertions, 0 deletions