git: hammer2 - Start work on inode indexing - MAJOR CHANGE

[Matthew Dillon]

commit cf1b3fafd1f08bd3a18fc9af3c431c48f600eb32
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date:   Sat Jun 18 22:01:00 2016 -0700

    hammer2 - Start work on inode indexing - MAJOR CHANGE
    
    A major change to how inodes work is required to allow NFS exports to be
    supported and also to make mirroring operations optimal.  Both needs are
    met by indexing most inodes so they can be looked up by inode number.  I've
    tried to avoid having to do this for well over 2 years now but I finally
    came to the conclusion that necessary features and efficiencies are
    impossible without it.
    
    + For NFS exports we have to be able to lookup a file by inode number in
      order to be able to translate NFS file handles.
    
    + Mirroring, Multi-Master, and other Multi-Node operations are extremely
      inefficient when a large file or (even worse) some high-level directory
      is renamed, because the synchronization code cannot be made aware of the
      rename.  The synchronizer winds up making a copy of the file or the
      directory subhierarchy and that can be disaster if it winds up being
      terrabytes.
    
    To solve these problems we treat nearly ALL directory entries as hardlink
    targets and place the hardlink target at the root of the PFS.  This puts
    nearly all inodes in a readily accessible place indexed by inode number.
    This means we can now implement inode number lookups for NFS, and it also
    means that the synchronizer does not have to copy anything when a file or
    directory is renamed.
    
    * Implement these changes by using an abbreviated version of the hardlink
      target code that we already have.  Get rid of the common-parent-directory
      code (we will use the PFS iroot), and force almost everything to be a
      hardlink.
    
    * device nodes and softlinks are excepted.  These work as they did before,
      created in the directory entry itself and not as a hardlinked inode.
      I might have to make these hardlink targets in the future too but at
      the moment it looks avoidable.
    
    * Unfortunately, this change creates a number of REGRESSIONS:
    
      (1) There are now two inodes per file instead of one.  The real inode
          indexed in the PFS root, and the hardlink pointer in the directory
          entry.  This eats another 1KB.
    
      (2) We lose a bunch of sequential layout optimizations (for the moment),
          particularly when stat()ing directory entries.
    
      (3) Inode creation and deletion ops will unfortunately cause more SMP
          conflicts due to all the inodes being indexed in one place.

Summary of changes:
 sys/vfs/hammer2/hammer2.h       |   3 +-
 sys/vfs/hammer2/hammer2_admin.c |  12 ++++
 sys/vfs/hammer2/hammer2_inode.c |  33 +++++++--
 sys/vfs/hammer2/hammer2_vnops.c | 149 ++++++++++++++++++----------------------
 sys/vfs/hammer2/hammer2_xops.c  |   2 +
 5 files changed, 108 insertions(+), 91 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/cf1b3fafd1f08bd3a18fc9af3c431c48f600eb32


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