Re: Break 2.4 VM in five easy steps

[Eric W. Biederman]

Mike Galbraith <[e-mail]> writes:

> On 6 Jun 2001, Eric W. Biederman wrote:
> 
> > Derek Glidden <[e-mail]> writes:
> >
> >
> > > The problem I reported is not that 2.4 uses huge amounts of swap but
> > > that trying to recover that swap off of disk under 2.4 can leave the
> > > machine in an entirely unresponsive state, while 2.2 handles identical
> > > situations gracefully.
> > >
> >
> > The interesting thing from other reports is that it appears to be kswapd
> > using up CPU resources.  Not the swapout code at all.  So it appears
> > to be a fundamental VM issue.  And calling swapoff is just a good way
> > to trigger it.
> >
> > If you could confirm this by calling swapoff sometime other than at
> > reboot time.  That might help.  Say by running top on the console.
> 
> The thing goes comatose here too. SCHED_RR vmstat doesn't run, console
> switch is nogo...
> 
> After running his memory hog, swapoff took 18 seconds.  I hacked a
> bleeder valve for dead swap pages, and it dropped to 4 seconds.. still
> utterly comatose for those 4 seconds though.

At the top of the while(1) loop in try_to_unuse what happens if you put in.
if (need_resched) schedule(); 
It should be outside all of the locks.  It might just be a matter of everything
serializing on the SMP locks, and the kernel refusing to preempt itself.

Eric