Re: [PATCH 1/2] [REPOST] mm: show node to memory section relationship with symlinks in sysfs

On Fri, 10 Oct 2008 16:18:44 -0700
Gary Hade <garyhade@xxxxxxxxxx> wrote:

On Fri, Oct 10, 2008 at 02:59:50PM -0700, Andrew Morton wrote:
On Fri, 10 Oct 2008 14:33:57 -0700
Gary Hade <garyhade@xxxxxxxxxx> wrote:

On Fri, Oct 10, 2008 at 12:42:39PM -0700, Andrew Morton wrote:
On Thu, 9 Oct 2008 12:21:15 -0700
Gary Hade <garyhade@xxxxxxxxxx> wrote:

Show node to memory section relationship with symlinks in sysfs

Add /sys/devices/system/node/nodeX/memoryY symlinks for all
the memory sections located on nodeX. For example:
/sys/devices/system/node/node1/memory135 -> ../../memory/memory135
indicates that memory section 135 resides on node1.

I'm not seeing here a description of why the kernel needs this feature.
Why is it useful? How will it be used? What value does it have to
our users?

Sorry, I should have included that. In our case, it is another
small step towards eventual total node removal. We will need to
know which memory sections to offline for whatever node is targeted
for removal. However, I suspect that exposing the node to section
information to user-level could be useful for other purposes.
For example, I have been thinking that using memory hotremove
functionality to modify the amount of available memory on specific
nodes without having to physically add/remove DIMMs might be useful
to those that test application or benchmark performance on a
multi-node system in various memory configurations.


hm, OK, thanks. It does sound a bit thin, and if we merge this then
not only do we get a porkier kernel,

Would you feel the same about the size increase if patch 2/2 (include
memory section subtree in sysfs with only sparsemem enabled) was
withdrawn?

Without patch 2/2 the size increase for non-Sparsemem or Sparsemem
wo/memory hotplug kernels is extremely small. Even for memory hotplug
enabled kernels there is only a little extra code in ./drivers/base/node.o
which only gets linked into NUMA enabled kernels. I can gather some numbers
if necessary.

Size is probably a minor issue on memory-hotpluggable machines.

we also get a new userspace interface which we're then locked into.

True.

That's a bigger issue. The later we leave this sort of thing, the more
information we have.

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