Re: where did all my memory go?

On Wed, 2005-02-16 at 14:57 -0600, Eric Anderson wrote:
> Brooks Davis wrote:
> > On Wed, Feb 16, 2005 at 12:12:10PM -0800, Sean McNeil wrote:
> > 
> >>With a system built yesterday on my amd64, I had plenty of memory
> >>showing as free when the system completely started up.  Even after
> >>intense usage I showed lots of free memory in top.  Over night at some
> >>point all my memory is no longer free but inactive.  Is there anything
> >>wrong here or is this expected behavior?  ps doesn't show any serious
> >>usage by any particular process.  Also, if disk caches or something were
> >>taking up the memory, I would expect it to have shown a lot earlier.
> > 
> > 
> > On a system that has been up for any significant time, free memory
> > should be very small since free memory is wasted.  My guess is that it
> > is disk cache and that one of the nightly jobs accessed enough stuff to
> > fill it.
> 
> Speaking of this - is there a way to flush the disk cache?  

I would have to dispute this fact.  Any disk cache should not be
assigned to inactive user pages.  It should be, IMHO, cache or buffer
memory.  In my original email, the vmstat -m output would support this:

  UFS dirhash  2656  1105K   1330K    15744  16,32,64,128,256,512,1024,2048
   BIO buffer  5435 10870K  10940K   236537  2048

I see nothing on my system that comes close to accounting for the 1G of
inactive memory.  Further, it really makes something like the system
applet in gnome useless when all my memory is claimed to be allocated as
user space.  I've only recently used this applet, but again I stress
that after heavy usage of the system during initial boot I had plenty of
ram shown as free.

As for flushing the disk cache, I thought that sync should do this.  It
doesn't have any effect here, though.

Cheers,
Sean