freebsd-nq

History

Jeff Roberson 767b9a529d - Cleanup unlocked accesses to buf flags by introducing a new b_vflag member that is protected by the vnode lock. - Move B_SCANNED into b_vflags and call it BV_SCANNED. - Create a vop_stdfsync() modeled after spec's sync. - Replace spec_fsync, msdos_fsync, and hpfs_fsync with the stdfsync and some fs specific processing. This gives all of these filesystems proper behavior wrt MNT_WAIT/NOWAIT and the use of the B_SCANNED flag. - Annotate the locking in buf.h		2003-02-09 11:28:35 +00:00
..
ffs_alloc.c	Bow to the whining masses and change a union back into void *. Retain	2003-01-13 00:33:17 +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	Move the allocation of the inode contents into ffs_vfsops.c rather than	2002-12-27 10:23:03 +00:00
ffs_inode.c	Remove M_TRYWAIT/M_WAITOK/M_WAIT. Callers should use 0.	2003-01-21 08:56:16 +00:00
ffs_snapshot.c	Remove M_TRYWAIT/M_WAITOK/M_WAIT. Callers should use 0.	2003-01-21 08:56:16 +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	Remove M_TRYWAIT/M_WAITOK/M_WAIT. Callers should use 0.	2003-01-21 08:56:16 +00:00
ffs_subr.c	Move the allocation of the inode contents into ffs_vfsops.c rather than	2002-12-27 10:23:03 +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	Remove M_TRYWAIT/M_WAITOK/M_WAIT. Callers should use 0.	2003-01-21 08:56:16 +00:00
ffs_vnops.c	- Cleanup unlocked accesses to buf flags by introducing a new b_vflag member	2003-02-09 11:28:35 +00:00
fs.h	o Improve wording of the comment that accompanies fs_pad. The	2003-01-10 06:59:34 +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	Add support to UFS2 to provide storage for extended attributes.	2002-07-19 07:29:39 +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