Module Name:	basesrc
Committed By:	lukem
Date:		Thu Sep  6 02:16:02 UTC 2001

Modified Files:
	basesrc/sbin/fsck_ffs: setup.c
	basesrc/sbin/newfs: extern.h mkfs.c newfs.8 newfs.c
	basesrc/sbin/tunefs: tunefs.8 tunefs.c
	basesrc/usr.sbin/dumpfs: dumpfs.c
	syssrc/sys/ufs/ffs: ffs_alloc.c ffs_bswap.c ffs_vfsops.c fs.h

Log Message:
Incorporate the enhanced ffs_dirpref() by Grigoriy Orlov, as found in
FreeBSD (three commits; the initial work, man page updates, and a fix
to ffs_reload()), with the following differences:
- Be consistent between newfs(8) and tunefs(8) as to the options which
  set and control the tuning parameters for this work (avgfilesize & avgfpdir)
- Use u_int16_t instead of u_int8_t to keep track of the number of
  contiguous directories (suggested by Chuck Silvers)
- Work within our FFS_EI framework
- Ensure that fs->fs_maxclusters and fs->fs_contigdirs don't point to
  the same area of memory

The new algorithm has a marked performance increase, especially when
performing tasks such as untarring pkgsrc.tar.gz, etc.

The original FreeBSD commit messages are attached:

=====
mckusick    2001/04/10 01:39:00 PDT
  Directory layout preference improvements from Grigoriy Orlov <gluk@ptci.ru>.
  His description of the problem and solution follow. My own tests show
  speedups on typical filesystem intensive workloads of 5% to 12% which
  is very impressive considering the small amount of code change involved.

  ------

    One day I noticed that some file operations run much faster on
  small file systems then on big ones. I've looked at the ffs
  algorithms, thought about them, and redesigned the dirpref algorithm.

    First I want to describe the results of my tests. These results are old
  and I have improved the algorithm after these tests were done. Nevertheless
  they show how big the perfomance speedup may be. I have done two file/directory
  intensive tests on a two OpenBSD systems with old and new dirpref algorithm.
  The first test is "tar -xzf ports.tar.gz", the second is "rm -rf ports".
  The ports.tar.gz file is the ports collection from the OpenBSD 2.8 release.
  It contains 6596 directories and 13868 files. The test systems are:

  1. Celeron-450, 128Mb, two IDE drives, the system at wd0, file system for
     test is at wd1. Size of test file system is 8 Gb, number of cg=991,
     size of cg is 8m, block size = 8k, fragment size = 1k OpenBSD-current
     from Dec 2000 with BUFCACHEPERCENT=35

  2. PIII-600, 128Mb, two IBM DTLA-307045 IDE drives at i815e, the system
     at wd0, file system for test is at wd1. Size of test file system is 40 Gb,
     number of cg=5324, size of cg is 8m, block size = 8k, fragment size = 1k
     OpenBSD-current from Dec 2000 with BUFCACHEPERCENT=50

  You can get more info about the test systems and methods at:
  http://www.ptci.ru/gluk/dirpref/old/dirpref.html

                                Test Results

               tar -xzf ports.tar.gz               rm -rf ports
    mode  old dirpref new dirpref speedup old dirprefnew dirpref speedup
                               First system
   normal     667         472      1.41       477        331       1.44
   async      285         144      1.98       130         14       9.29
   sync       768         616      1.25       477        334       1.43
   softdep    413         252      1.64       241         38       6.34
                               Second system
   normal     329         81       4.06       263.5       93.5     2.81
   async      302         25.7    11.75       112          2.26   49.56
   sync       281         57.0     4.93       263         90.5     2.9
   softdep    341         40.6     8.4        284          4.76   59.66

  "old dirpref" and "new dirpref" columns give a test time in seconds.
  speedup - speed increasement in times, ie. old dirpref / new dirpref.

  ------

  Algorithm description

  The old dirpref algorithm is described in comments:

  /*
   * Find a cylinder to place a directory.
   *
   * The policy implemented by this algorithm is to select from
   * among those cylinder groups with above the average number of
   * free inodes, the one with the smallest number of directories.
   */

  A new directory is allocated in a different cylinder groups than its
  parent directory resulting in a directory tree that is spreaded across
  all the cylinder groups. This spreading out results in a non-optimal
  access to the directories and files. When we have a small filesystem
  it is not a problem but when the filesystem is big then perfomance
  degradation becomes very apparent.

  What I mean by a big file system ?

    1. A big filesystem is a filesystem which occupy 20-30 or more percent
       of total drive space, i.e. first and last cylinder are physically
       located relatively far from each other.
    2. It has a relatively large number of cylinder groups, for example
       more cylinder groups than 50% of the buffers in the buffer cache.

  The first results in long access times, while the second results in
  many buffers being used by metadata operations. Such operations use
  cylinder group blocks and on-disk inode blocks. The cylinder group
  block (fs->fs_cblkno) contains struct cg, inode and block bit maps.
  It is 2k in size for the default filesystem parameters. If new and
  parent directories are located in different cylinder groups then the
  system performs more input/output operations and uses more buffers.
  On filesystems with many cylinder groups, lots of cache buffers are
  used for metadata operations.

  My solution for this problem is very simple. I allocate many directories
  in one cylinder group. I also do some things, so that the new allocation
  method does not cause excessive fragmentation and all directory inodes
  will not be located at a location far from its file's inodes and data.
  The algorithm is:
  /*
   * Find a cylinder group to place a directory.
   *
   * The policy implemented by this algorithm is to allocate a
   * directory inode in the same cylinder group as its parent
   * directory, but also to reserve space for its files inodes
   * and data. Restrict the number of directories which may be
   * allocated one after another in the same cylinder group
   * without intervening allocation of files.
   *
   * If we allocate a first level directory then force allocation
   * in another cylinder group.
   */

    My early versions of dirpref give me a good results for a wide range of
  file operations and different filesystem capacities except one case:
  those applications that create their entire directory structure first
  and only later fill this structure with files.

    My solution for such and similar cases is to limit a number of
  directories which may be created one after another in the same cylinder
  group without intervening file creations. For this purpose, I allocate
  an array of counters at mount time. This array is linked to the superblock
  fs->fs_contigdirs[cg]. Each time a directory is created the counter
  increases and each time a file is created the counter decreases. A 60Gb
  filesystem with 8mb/cg requires 10kb of memory for the counters array.

    The maxcontigdirs is a maximum number of directories which may be created
  without an intervening file creation. I found in my tests that the best
  performance occurs when I restrict the number of directories in one cylinder
  group such that all its files may be located in the same cylinder group.
  There may be some deterioration in performance if all the file inodes
  are in the same cylinder group as its containing directory, but their
  data partially resides in a different cylinder group. The maxcontigdirs
  value is calculated to try to prevent this condition. Since there is
  no way to know how many files and directories will be allocated later
  I added two optimization parameters in superblock/tunefs. They are:

          int32_t  fs_avgfilesize;   /* expected average file size */
          int32_t  fs_avgfpdir;      /* expected # of files per directory */

  These parameters have reasonable defaults but may be tweeked for special
  uses of a filesystem. They are only necessary in rare cases like better
  tuning a filesystem being used to store a squid cache.

  I have been using this algorithm for about 3 months. I have done
  a lot of testing on filesystems with different capacities, average
  filesize, average number of files per directory, and so on. I think
  this algorithm has no negative impact on filesystem perfomance. It
  works better than the default one in all cases. The new dirpref
  will greatly improve untarring/removing/coping of big directories,
  decrease load on cvs servers and much more. The new dirpref doesn't
  speedup a compilation process, but also doesn't slow it down.

  Obtained from:	Grigoriy Orlov <gluk@ptci.ru>
=====

=====
iedowse     2001/04/23 17:37:17 PDT
  Pre-dirpref versions of fsck may zero out the new superblock fields
  fs_contigdirs, fs_avgfilesize and fs_avgfpdir. This could cause
  panics if these fields were zeroed while a filesystem was mounted
  read-only, and then remounted read-write.

  Add code to ffs_reload() which copies the fs_contigdirs pointer
  from the previous superblock, and reinitialises fs_avgf* if necessary.

  Reviewed by:	mckusick
=====

=====
nik         2001/04/10 03:36:44 PDT
  Add information about the new options to newfs and tunefs which set the
  expected average file size and number of files per directory.  Could do
  with some fleshing out.
=====


To generate a diff of this commit:
cvs rdiff -r1.48 -r1.49 basesrc/sbin/fsck_ffs/setup.c
cvs rdiff -r1.5 -r1.6 basesrc/sbin/newfs/extern.h
cvs rdiff -r1.54 -r1.55 basesrc/sbin/newfs/mkfs.c
cvs rdiff -r1.32 -r1.33 basesrc/sbin/newfs/newfs.8
cvs rdiff -r1.46 -r1.47 basesrc/sbin/newfs/newfs.c
cvs rdiff -r1.25 -r1.26 basesrc/sbin/tunefs/tunefs.8
cvs rdiff -r1.23 -r1.24 basesrc/sbin/tunefs/tunefs.c
cvs rdiff -r1.29 -r1.30 basesrc/usr.sbin/dumpfs/dumpfs.c
cvs rdiff -r1.49 -r1.50 syssrc/sys/ufs/ffs/ffs_alloc.c
cvs rdiff -r1.12 -r1.13 syssrc/sys/ufs/ffs/ffs_bswap.c
cvs rdiff -r1.84 -r1.85 syssrc/sys/ufs/ffs/ffs_vfsops.c
cvs rdiff -r1.19 -r1.20 syssrc/sys/ufs/ffs/fs.h

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.