Re: Please test: workaround to help swapoff behaviour

[Marcelo Tosatti <marcelo@conectiva.com.br>]

On Thu, 7 Jun 2001, Bulent Abali wrote:

> 
> I tested your patch against 2.4.5.  It works.  No more lockups.  Without
> the
> patch it took 14 minutes 51 seconds to complete swapoff (this is to recover
> 1.5GB of
> swap space).  During this time the system was frozen.  No keyboard, no
> screen, etc. Practically locked-up.
> 
> With the patch there are no more lockups. Swapoff kept running in the
> background.
> This is a winner.
>
> But here is the caveat: swapoff keeps burning 100% of the cycles until it
> completes.

Yup. Wait a while until the dead swap cache issue is sorted out. 

When that finally happens, the time spent in swapoff will probably be
"acceptable".

> This is not going to be a big deal during shutdowns.  Only when you enter
> swapoff from
> the command line it is going to be a problem.
> 
> I looked at try_to_unuse in swapfile.c.  I believe that the algorithm is
> broken.

Yes. 

> For each and every swap entry it is walking the entire process list
> (for_each_task(p)).  It is also grabbing a whole bunch of locks
> for each swap entry.  It might be worthwhile processing swap entries in
> batches instead of one entry at a time.

The real fix is to make the processing the other way around --- go looking
into the pte's and from there do the swapins. 

Don't have the time to do everything, though. :) 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/