freebsd-nq

History

Jeff Roberson 09f11da5a3 - Remove a race between fsync like functions and flushbufqueues() by requiring locked bufs in vfs_bio_awrite(). Previously the buf could have been written out by fsync before we acquired the buf lock if it weren't for giant. The cluster_wbuild() handles this race properly but the single write at the end of vfs_bio_awrite() would not. - Modify flushbufqueues() so there is only one copy of the loop. Pass a parameter in that says whether or not we should sync bufs with deps. - Call flushbufqueues() a second time and then break if we couldn't find any bufs without deps.		2003-03-13 07:19:23 +00:00
..
ffs_alloc.c	- Add a new 'flags' parameter to getblk().	2003-03-04 00:04:44 +00:00
ffs_balloc.c	- Add a new 'flags' parameter to getblk().	2003-03-04 00:04:44 +00:00
ffs_extern.h	This patch fixes a bug on an active filesystem on which a snapshot	2003-02-22 00:29:51 +00:00
ffs_inode.c	- Add a new 'flags' parameter to getblk().	2003-03-04 00:04:44 +00:00
ffs_snapshot.c	Use the appropriate size when zeroing out the unused portion	2003-03-07 23:49:16 +00:00
ffs_softdep_stub.c
ffs_softdep.c	- Add a new 'flags' parameter to getblk().	2003-03-04 00:04:44 +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
ffs_vfsops.c	- Add a new 'flags' parameter to getblk().	2003-03-04 00:04:44 +00:00
ffs_vnops.c	- Remove a race between fsync like functions and flushbufqueues() by	2003-03-13 07:19:23 +00:00
fs.h	This patch fixes a bug in the logical block calculation macros so	2003-02-22 00:19:26 +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

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