Re: Break 2.4 VM in five easy steps

[Jeffrey W. Baker]

On Wed, 6 Jun 2001, Andrew Morton wrote:

> "Jeffrey W. Baker" wrote:
> >
> > Because the 2.4 VM is so broken, and
> > because my machines are frequently deeply swapped,
>
> The swapoff algorithms in 2.2 and 2.4 are basically identical.
> The problem *appears* worse in 2.4 because it uses lots
> more swap.
>
> > they can sometimes take over 30 minutes to shutdown.
>
> Yes. The sys_swapoff() system call can take many minutes
> of CPU time.  It basically does:
>
> 	for (each page in swap device) {
> 		for (each process) {
> 			for (each page used by this process)
> 				stuff

Sure, and at shutdown time when swapoff is called, there is only 1
process, init, which isn't swapped out anymore.  So this should run like
lightning.

Repeat: something is horribly wrong with the VM's management of pages,
lists, swap, cache, etc.

-jwb