On Thu, Nov 16, 2006 at 03:28:29PM -0500, Blair Sadewitz wrote:
>
> I've noticed that if I untar a lot of files on an LFS filesystem,
> toward the very end of the untar (when all files in the archive are
> listed with -v but before it finishes), tar consumes 95%+ CPU for a
> few minutes and things get VERY slow.  This does not happen on FFS
> filesystems.  Is this just the nature of LFS, a bug, or do I have
> something set up incorrectly?  I got my lfs bsize from the -A option
> (2949k).

It's a problem with the code that flushes pending writes.  Your system
has a lot of free RAM, I expect.

If you look at the I/O statistics for that disk using "systat vmstat"
or iostat while the system is being slow, how many megs/sec is it
writing?  You could try this:

1) Take a rough estimate of your disk's write bandwidth in bytes/sec.
   Let's say it's 30000000.

2) Divide this by 4096 (on i386) to get pages, 7324 in this case.

3) Divide this by 4, a fudge factor chosen by means I can't explain
   well in a short email message, yielding 1831.

4) Check that 1831 * 4096 is larger than your segment size.  Since it's
   about 7.5MB, you're safe.

5) sysctl -w vfs.lfs.pagetrip=1831

Let me know what the results look like.

-- 
Thor Lancelot Simon	                                     tls@rek.tjls.com
  "The liberties...lose much of their value whenever those who have greater
   private means are permitted to use their advantages to control the course
   of public debate."					-John Rawls