freebsd-dev/sys/ufs/ffs
Robert Watson 763bbd2f4f Slightly change the semantics of vnode labels for MAC: rather than
"refreshing" the label on the vnode before use, just get the label
right from inception.  For single-label file systems, set the label
in the generic VFS getnewvnode() code; for multi-label file systems,
leave the labeling up to the file system.  With UFS1/2, this means
reading the extended attribute during vfs_vget() as the inode is
pulled off disk, rather than hitting the extended attributes
frequently during operations later, improving performance.  This
also corrects sematics for shared vnode locks, which were not
previously present in the system.  This chances the cache
coherrency properties WRT out-of-band access to label data, but in
an acceptable form.  With UFS1, there is a small race condition
during automatic extended attribute start -- this is not present
with UFS2, and occurs because EAs aren't available at vnode
inception.  We'll introduce a work around for this shortly.

Approved by:	re
Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, Network Associates Laboratories
2002-10-26 14:38:24 +00:00
..
ffs_alloc.c intmax_t is printed with %jd, not %lld. 2002-09-19 03:55:30 +00:00
ffs_balloc.c This update is a performance improvement when allocating blocks on 2002-10-22 01:14:25 +00:00
ffs_extern.h Introduce typedefs for the member functions of struct vfsops and employ 2002-08-13 10:05:50 +00:00
ffs_inode.c - Convert locks to use standard macros. 2002-09-25 02:49:48 +00:00
ffs_snapshot.c Within ufs, the ffs_sync and ffs_fsync functions did not always 2002-10-25 00:20:37 +00:00
ffs_softdep_stub.c Add a missing argument to the stub for softdep_setup_freeblocks. 2002-07-20 04:07:15 +00:00
ffs_softdep.c We must be careful to avoid recursive copy-on-write faults when 2002-10-23 21:47:02 +00:00
ffs_subr.c I forgot this bit of uglyness in the fsck_ffs cleanup. 2002-07-31 07:01:18 +00:00
ffs_tables.c This commit adds basic support for the UFS2 filesystem. The UFS2 2002-06-21 06:18:05 +00:00
ffs_vfsops.c Slightly change the semantics of vnode labels for MAC: rather than 2002-10-26 14:38:24 +00:00
ffs_vnops.c Fix a file-rewrite performance case for UFS[2]. When rewriting portions 2002-10-18 22:52:41 +00:00
fs.h Define two new superblock file system flags: 2002-10-14 17:07:11 +00:00
README.snapshot Fix a type: s/your are/you are/ 2002-07-12 19:56:31 +00:00
README.softupdates
softdep.h Add support to UFS2 to provide storage for extended attributes. 2002-07-19 07:29:39 +00:00

$FreeBSD$

Using Soft Updates

To enable the soft updates feature in your kernel, add option
SOFTUPDATES to your kernel configuration.

Once you are running a kernel with soft update support, you need to enable
it for whichever filesystems you wish to run with the soft update policy.
This is done with the -n option to tunefs(8) on the UNMOUNTED filesystems,
e.g. from single-user mode you'd do something like:

	tunefs -n enable /usr

To permanently enable soft updates on the /usr filesystem (or at least
until a corresponding ``tunefs -n disable'' is done).


Soft Updates Copyright Restrictions

As of June 2000 the restrictive copyright has been removed and 
replaced with a `Berkeley-style' copyright. The files implementing
soft updates now reside in the sys/ufs/ffs directory and are
compiled into the generic kernel by default.


Soft Updates Status

The soft updates code has been running in production on many
systems for the past two years generally quite successfully.
The two current sets of shortcomings are:

1) On filesystems that are chronically full, the two minute lag
   from the time a file is deleted until its free space shows up
   will result in premature filesystem full failures. This
   failure mode is most evident in small filesystems such as
   the root. For this reason, use of soft updates is not
   recommended on the root filesystem.

2) If your system routines runs parallel processes each of which
   remove many files, the kernel memory rate limiting code may
   not be able to slow removal operations to a level sustainable
   by the disk subsystem. The result is that the kernel runs out
   of memory and hangs.

Both of these problems are being addressed, but have not yet
been resolved. There are no other known problems at this time.


How Soft Updates Work

For more general information on soft updates, please see:
	http://www.mckusick.com/softdep/
	http://www.ece.cmu.edu/~ganger/papers/CSE-TR-254-95/

--
Marshall Kirk McKusick <mckusick@mckusick.com>
July 2000