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SubjectRe: [PATCH] change zonelist order v5 [1/3] implements zonelist order selection
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On Tue, 2007-05-08 at 11:05 -0700, Christoph Lameter wrote:
> On Tue, 8 May 2007, Lee Schermerhorn wrote:
>
> > > So far testing is IA64 only?
> > Yes, so far. I will test on an Opteron platform this pm.
> > Assume that no news is good news.
>
> A better assumption: no news -> no testing.

Before you asked, yes. I meant after the last message, if you didn't
hear from me, everything worked fine. And it does, sort of...


> You probably need a
> configuration with a couple of nodes. Maybesomething less symmetric than
> Kame? I.e. have 4GB nodes and then DMA32 takes out a sizeable chunk of it?
>

I tested on a 2 socket, 4GB Opteron blade. All memory is either DMA32
or DMA. I added some ad hoc instrumentation to the build_zonelist_*
functions to see what's happening. I have verified that the patches
appear to build the zonelists correctly:

default -> node order, because "low_kmem" [DMA+DMA32] > total_mem/2.
Zone lists:
DMA: DMA-0
DMA32: DMA32-0, DMA-0, DMA32-1
Normal: same as DMA32 [no normal memory]
Movable: same as DMA32 & Normal

explicit zone order also builds as expected:
DMA: DMA-0
DMA32: DMA32-1, DMA32-0, DMA-0
and same for normal and movable

However, a curious thing happens: in either order, allocations seem to
overflow to the remote DMA32 before dipping into the DMA!!!? I'm using
memtoy to create a large [3+GB] anon segment and locking it down.

I need to check a non-patched kernel to see if it behaves the same way,
and examine the code to see why... For one thing, the kernel seems to
do a bit better at reclaiming memory before overflowing. Eventually, it
will dip into DMA and finally get killed--OOM.

I'll be off-line most of the rest of the week, so I probably won't get
to investigate much further nor test on a larger socket count/memory
system until next week.

Lee



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