Re: [PATCH/RFC] Add node 'states' sysfs class attribute - V2

[Christoph Lameter <clameter@sgi.com>]

On Mon, 27 Aug 2007, Andrew Morton wrote:

> > The masks can get quite ugly to read if you have lots of nodes. F.e. with 
> > 1024 nodes you get a line that wraps around more than 10 times.
> 
> So don't read them - use a program to turn them into your preferred
> human-readable representation.

You are volunterring to write all the programs we need for this and that 
debugging situation? Even if you do this: It will significantly slow us 
down always having to come to you and ask you for a tool.

> We see this often, btw.  People want nice and easy-to-read kernel->human
> interfaces because the tool of choice for displaying these things to humans
> is "cat".  How lame is that?
> 
> I do think that a sysfs interface like this should be optimised for
> kernel->program communication, not for kernel->human.

Well I keep ending up cat this and that proc entry for debugging and its 
difficult to do if one sysfs file spews huge amounts of illegible binary 
data to you.

I do not think that tools would have trouble deciphering that format. It 
is going to be more compact and easier to handle to have the node ranges 
rather than converting a list of binaries. Lee already noted the 
huge amounts of zeros that he got.

> > > OK, well if the meminfo file is the only one in there which broke the
> > > golden rule, I don't think we have sufficient excuse to break it again.
> > > 
> > > $ cat  /sys/devices/system/node/possible
> > > 0-4
> > > $
> > > 
> > > I think a bitmap would be better, personally.
> > > 
> > > That in fact makes "possible" unneeded, doesn't it?  It would always be
> > > all-ones?
> > 
> > There could be the case that nodes 1-9 and 20-29 are possible but 
> > the ones in between are not available.
> 
> OK.
> 
> How do we communicate to userspace what is the maximum number of nodes
> which this kernel supports?  That would be (1<<CONFIG_NODES_SHIFT), I
> guess.  Or maybe we don't care?

The last node mentioned in possible is the highest. That will be difficult 
to see if you want the kernel developers to read binary numbers but I 
guess we have to be tough.

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