freebsd-skq

History

jhb 279b2b8278 Locking for the per-process resource limits structure. - struct plimit includes a mutex to protect a reference count. The plimit structure is treated similarly to struct ucred in that is is always copy on write, so having a reference to a structure is sufficient to read from it without needing a further lock. - The proc lock protects the p_limit pointer and must be held while reading limits from a process to keep the limit structure from changing out from under you while reading from it. - Various global limits that are ints are not protected by a lock since int writes are atomic on all the archs we support and thus a lock wouldn't buy us anything. - All accesses to individual resource limits from a process are abstracted behind a simple lim_rlimit(), lim_max(), and lim_cur() API that return either an rlimit, or the current or max individual limit of the specified resource from a process. - dosetrlimit() was renamed to kern_setrlimit() to match existing style of other similar syscall helper functions. - The alpha OSF/1 compat layer no longer calls getrlimit() and setrlimit() (it didn't used the stackgap when it should have) but uses lim_rlimit() and kern_setrlimit() instead. - The svr4 compat no longer uses the stackgap for resource limits calls, but uses lim_rlimit() and kern_setrlimit() instead. - The ibcs2 compat no longer uses the stackgap for resource limits. It also no longer uses the stackgap for accessing sysctl's for the ibcs2_sysconf() syscall but uses kernel_sysctl() instead. As a result, ibcs2_sysconf() no longer needs Giant. - The p_rlimit macro no longer exists. Submitted by: mtm (mostly, I only did a few cleanups and catchups) Tested on: i386 Compiled on: alpha, amd64		2004-02-04 21:52:57 +00:00
..
ffs_alloc.c	Tweak the calculation of minbfree in ffs_dirpref() so that only	2003-10-31 07:25:06 +00:00
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	This patch fixes a bug on an active filesystem on which a snapshot	2003-02-22 00:29:51 +00:00
ffs_inode.c	DuH!	2003-10-18 14:10:28 +00:00
ffs_rawread.c	Send B_PHYS out to pasture, it no longer serves any function.	2003-11-15 09:28:09 +00:00
ffs_snapshot.c	Avoid calling vprint on a vnode while holding its interlock mutex.	2004-01-04 04:08:34 +00:00
ffs_softdep_stub.c	Use __FBSDID().	2003-06-11 06:34:30 +00:00
ffs_softdep.c	Move the P_COWINPROGRESS flag from being a per-process p_flag to being a	2003-10-23 21:14:08 +00:00
ffs_subr.c	Use __FBSDID().	2003-06-11 06:34:30 +00:00
ffs_tables.c	Use __FBSDID().	2003-06-11 06:34:30 +00:00
ffs_vfsops.c	Set fs_ronly to the correct value in ffs_reload() when reloading the file	2003-12-07 05:16:52 +00:00
ffs_vnops.c	Locking for the per-process resource limits structure.	2004-02-04 21:52:57 +00:00
fs.h	Write the UFS2 superblock with a 'BAD' magic number at the beginning	2003-11-16 07:08:27 +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	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