Re: [RFC][PATCH 2/9] deadlock prevention core

From: Andrew Morton
Date: Mon Aug 14 2006 - 01:26:46 EST

On Mon, 14 Aug 2006 07:03:55 +0200
Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:

> On Sun, 2006-08-13 at 21:58 -0700, Andrew Morton wrote:
> > On Mon, 14 Aug 2006 06:40:53 +0200
> > Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> >
> > > Testcase:
> > >
> > > Mount an NBD device as sole swap device and mmap > physical RAM, then
> > > loop through touching pages only once.
> >
> > Fix: don't try to swap over the network. Yes, there may be some scenarios
> > where people have no local storage, but it's reasonable to expect anyone
> > who is using Linux as an "enterprise storage platform" to stick a local
> > disk on the thing for swap.
> I wish you were right, however there seems to be a large demand to go
> diskless and swap over iSCSI because disks seem to be the nr. 1 failing
> piece of hardware in systems these days.

We could track dirty anonymous memory and throttle.

Also, there must be some value of /proc/sys/vm/min_free_kbytes at which a
machine is no longer deadlockable with any of these tricks. Do we know
what level that is?

> > That leaves MAP_SHARED, but mm-tracking-shared-dirty-pages.patch will fix
> > that, will it not?
> Will makes it less likely. One can still have memory pressure, the
> remaining bits of memory can still get stuck in socket queues for
> blocked processes.

But there's lots of reclaimable pagecache around and kswapd will free it
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