freebsd-dev

History

Jeff Roberson 2f05568aa8 - Check the XLOCK before inspecting v_data. - Slightly rewrite the fsync loop to be more lock friendly. We must acquire the vnode interlock before dropping the mnt lock. We must also check XLOCK to prevent vclean() races. - Use LK_INTERLOCK in the vget() in ffs_sync to further prevent vclean() races. - Use a local variable to store the results of the nvp == TAILQ_NEXT test so that we do not access the vp after we've vrele()d it. - Add an XXX comment about UFS_UPDATE() not being protected by any lock here. I suspect that it should need the VOP lock.		2003-10-05 07:16:45 +00:00
..
ffs_alloc.c
ffs_balloc.c
ffs_extern.h
ffs_inode.c
ffs_rawread.c
ffs_snapshot.c	- Skip over xvp if XLOCK is set.	2003-10-05 06:48:37 +00:00
ffs_softdep_stub.c
ffs_softdep.c	- The VI assert in getdirtybuf() is only valid if we're not on a VCHR	2003-10-04 15:57:05 +00:00
ffs_subr.c
ffs_tables.c
ffs_vfsops.c	- Check the XLOCK before inspecting v_data.	2003-10-05 07:16:45 +00:00
ffs_vnops.c	Synchronize access to a vm page's valid field using the containing	2003-10-04 20:38:32 +00:00
fs.h
README.snapshot
README.softupdates
softdep.h

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