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SubjectRe: [patch] numa: fix BUILD_BUG_ON for node_read_distance
On Wed, 10 Mar 2010, Greg KH wrote:

> > node_read_distance() has a BUILD_BUG_ON() to prevent buffer overruns when
> > the number of nodes printed will exceed the buffer length.
> >
> > Each node only needs four chars: three for distance (maximum distance is
> > 255) and one for a seperating space or a trailing newline.
>
> Is this causing a problem as-is today that we need to resolve for
> 2.6.34? Or is this 2.6.35 material?
>

It's not needed at least for x86 for 2.6.34 since the max
CONFIG_NODES_SHIFT is 9. I don't know about other architectures with
different ranges or page sizes.

I'm going to push a change to the x86 maintainers to increase that max
CONFIG_NODES_SHIFT to 10 hopefully for 2.6.35, that's where we run into
this error.

> Who chose this original number, and why is it off by 1/2?
>

It's earlier than the git history, but there's no reason to divide
PAGE_SIZE in half. We've been running machines with this patch for well
over a year and /sys/devices/system/node/nodeN/distance works just fine
with 1K nodes.


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