freebsd-dev

History

Jeff Roberson a0ebaaddef - Don't acquire the vnode interlock in drain_output(). Instead, require the caller to acquire it. This permits drain_output() to be done atomically with other operations as well as reducing the number of lock operations. - Assert that the proper locks are held in drain_output(). - Change getdirtybuf() to accept a mutex as an argument. This mutex is used to protect the vnode's buf list and the BKGRDWAIT flag. This lock is dropped when we successfully acquire a buffer and held on return otherwise. These semantics reduce the number of cumbersome cases in calling code. - Pass the mtx from getdirtybuf() into interlocked_sleep() and allow this mutex to be used as the interlock argument to BUF_LOCK() in the LOCKBUF case of interlocked_sleep(). - Change the return value of getdirtybuf() to be the resulting locked buffer or NULL otherwise. This is for callers who pass in a list head that requires a lock. It is necessary since the lock that protects the list head must be dropped in getdirtybuf() so that we don't have a lock order reversal with the buf queues lock in bremfree(). - Adjust all callers of getdirtybuf() to match the new semantics. - Add a comment in indir_trunc() that points at unlocked access to a buf. This may also be one of the last instances of incore() in the tree.		2003-08-31 07:29:34 +00:00
..
ffs_alloc.c
ffs_balloc.c	Eliminate the i_devvp field from the incore UFS inodes, we can	2003-08-15 20:03:19 +00:00
ffs_extern.h
ffs_inode.c
ffs_rawread.c	The previous change necessitates the addition of a new #include. Otherwise,	2003-08-18 17:27:08 +00:00
ffs_snapshot.c
ffs_softdep_stub.c
ffs_softdep.c	- Don't acquire the vnode interlock in drain_output(). Instead, require the	2003-08-31 07:29:34 +00:00
ffs_subr.c
ffs_tables.c
ffs_vfsops.c	Eliminate the i_devvp field from the incore UFS inodes, we can	2003-08-15 20:03:19 +00:00
ffs_vnops.c	Consistently use the BSD u_int and u_short instead of the SYSV uint and	2003-08-07 15:04:27 +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