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Date: Tue, 18 Jun 2002 19:17:00 +0100 (BST)
From: Hugh Dickins <hugh@veritas.com>
To: "Richard B. Johnson" <root@chaos.analogic.com>
cc: DevilKin <devilkin-lkml@blindguardian.org>, linux-kernel@vger.kernel.org
Subject: Re: VMM - freeing up swap space
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On Tue, 18 Jun 2002, Richard B. Johnson wrote:
> On Tue, 18 Jun 2002, DevilKin wrote:
> > On Tuesday 18 June 2002 17:10, Richard B. Johnson wrote:
> > >
> > > Sure. Execute `swapoff -a`, followed by `swapon -a`. This is no joke.
> > 
> > Hmm. Now if you happen to get out of memory during the swapoff part, you'll 
> > get the OO killer on your tail? Or will the system just go freeze solid?
> 
> I think `swapoff -a` will just fail to remove the swap device/file(s) if
> it doesn't have the memory. I've done this with 16 Mb of RAM in the
> 'good-old-days', where VM was swap.

You're right that swapoff should just fail, but sadly we've not done
the work to make that so: the OOM-killer does indeed come in (and it's
not the swapoff task it attacks); and if that can't free enough, then
the system will freeze.

In what forum, by the way, may I suggest to distros that they "rm -rf"
in any tmpfs mounts before shutdown swapoff?  It avoids this OOM issue
at shutdown, plus it's a whole lot faster than doing the swapoff.

Hugh

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