freebsd-skq

History

jeff 02517b6731 - Replace v_flag with v_iflag and v_vflag - v_vflag is protected by the vnode lock and is used when synchronization with VOP calls is needed. - v_iflag is protected by interlock and is used for dealing with vnode management issues. These flags include X/O LOCK, FREE, DOOMED, etc. - All accesses to v_iflag and v_vflag have either been locked or marked with mp_fixme's. - Many ASSERT_VOP_LOCKED calls have been added where the locking was not clear. - Many functions in vfs_subr.c were restructured to provide for stronger locking. Idea stolen from: BSD/OS		2002-08-04 10:29:36 +00:00
..
ffs_alloc.c	- Replace v_flag with v_iflag and v_vflag	2002-08-04 10:29:36 +00:00
ffs_balloc.c	Add support to UFS2 to provide storage for extended attributes.	2002-07-19 07:29:39 +00:00
ffs_extern.h	Move ffs_isfreeblock() to ffs_alloc.c and make it static.	2002-07-30 11:54:48 +00:00
ffs_inode.c	Add support to UFS2 to provide storage for extended attributes.	2002-07-19 07:29:39 +00:00
ffs_snapshot.c	- Replace v_flag with v_iflag and v_vflag	2002-08-04 10:29:36 +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	- Replace v_flag with v_iflag and v_vflag	2002-08-04 10:29:36 +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	- Replace v_flag with v_iflag and v_vflag	2002-08-04 10:29:36 +00:00
ffs_vnops.c	- Replace v_flag with v_iflag and v_vflag	2002-08-04 10:29:36 +00:00
fs.h	This commit adds basic support for the UFS2 filesystem. The UFS2	2002-06-21 06:18:05 +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

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