freebsd-nq

History

Jeff Roberson 8e37fbad3a - Don't use atomic operations to deal with the active array, instead it is now quite naturally protected by the ufsmount mutex. - Use the ufs lock to protect various fields in struct fs, primarily the cg summary needs protection to avoid allocation races. Several functions have been slightly re-arranged to reduce the number of lock operations. - Adjust several functions (blkfree, freefile, etc.) to accept a ufsmount as an argument so that we may access the ufs lock. Sponsored By: Isilon Systems, Inc.		2005-01-24 10:08:35 +00:00
..
ffs_alloc.c	- Don't use atomic operations to deal with the active array, instead	2005-01-24 10:08:35 +00:00
ffs_balloc.c	Remove the unused credential argument from VOP_FSYNC() and VFS_SYNC().	2005-01-11 07:36:22 +00:00
ffs_extern.h	- Change some function parameters so that the ufsmount structure is	2005-01-24 10:02:11 +00:00
ffs_inode.c	- Acquire the ufs lock when manipulating some fields of struct fs.	2005-01-24 10:04:22 +00:00
ffs_rawread.c	Wrap the bufobj operations in macros: BO_STRATEGY() and BO_WRITE()	2005-01-11 09:10:46 +00:00
ffs_snapshot.c	Remove the unused credential argument from VOP_FSYNC() and VFS_SYNC().	2005-01-11 07:36:22 +00:00
ffs_softdep_stub.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
ffs_softdep.c	Remove the unused credential argument from VOP_FSYNC() and VFS_SYNC().	2005-01-11 07:36:22 +00:00
ffs_subr.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
ffs_tables.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
ffs_vfsops.c	Fix ACLs handling for the root file system.	2005-01-15 17:09:53 +00:00
ffs_vnops.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
fs.h	- Mark the struct fs members that require the ufsmount mutex.	2005-01-24 10:03:17 +00:00
README.snapshot	Remove the comment about dump(8) not working properly with snapshots.	2002-12-12 00:31:45 +00:00
README.softupdates
softdep.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00

README.softupdates

$FreeBSD$

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