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    SubjectRe: [PATCH 1/2] [REPOST] mm: show node to memory section relationship with symlinks in sysfs
    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@us.ibm.com> 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@us.ibm.com> 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    withdrawn?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.

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

    True.

    >
    > So I'm inclined to skip this change until we have a stronger need?

    Of course, I'm not. :)

    Gary

    --
    Gary Hade
    System x Enablement
    IBM Linux Technology Center
    503-578-4503 IBM T/L: 775-4503
    garyhade@us.ibm.com
    http://www.ibm.com/linux/ltc



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