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History

David Schultz 188f6433f6 When the softupdates worklist gets too long, threads that attempt to add more work are forced to process two worklist items first. However, processing an item may generate additional work, causing the unlucky thread to recursively process the worklist. Add a per-thread flag to detect this situation and avoid the recursion. This should fix the stack overflows that could occur while removing large directory trees. Tested by: kris Reviewed by: mckusick		2005-03-25 17:30:31 +00:00
..
ffs_alloc.c	The recomputation of file system summary at mount time can be a	2005-02-20 08:02:15 +00:00
ffs_balloc.c	For snapshots we need all VOP_LOCKs to be exclusive.	2005-02-08 16:25:50 +00:00
ffs_extern.h	Make a some SYSCTL_NODEs and some of FFS's VFS_ methods static.	2005-02-10 12:20:08 +00:00
ffs_inode.c	- Fix an assert now that the XLOCK no longer exists.	2005-03-13 12:00:41 +00:00
ffs_rawread.c	For snapshots we need all VOP_LOCKs to be exclusive.	2005-02-08 16:25:50 +00:00
ffs_snapshot.c	- The VI_DOOMED flag now signals the end of a vnode's relationship with	2005-03-13 12:01:50 +00:00
ffs_softdep.c	When the softupdates worklist gets too long, threads that attempt to	2005-03-25 17:30:31 +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	Add two arguments to the vfs_hash() KPI so that filesystems which do	2005-03-16 11:20:51 +00:00
ffs_vnops.c	- It is not legal to access v_data without the vnode lock or interlock	2005-03-13 12:04:12 +00:00
fs.h	The recomputation of file system summary at mount time can be a	2005-02-20 08:02:15 +00:00
README.snapshot
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