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    SubjectRe: [PATCH 1/3] powerpc: Allocate per-cpu areas for node IDs for SLQB to use as per-node areas
    On Mon, 21 Sep 2009 10:17:52 -0700 Daniel Walker wrote:

    > On Mon, 2009-09-21 at 17:10 +0100, Mel Gorman wrote:
    > > SLQB uses DEFINE_PER_CPU to define per-node areas. An implicit
    > > assumption is made that all valid node IDs will have matching valid CPU
    > > ids. In memoryless configurations, it is possible to have a node ID with
    > > no CPU having the same ID. When this happens, a per-cpu are is not
    > > created and the value of paca[cpu].data_offset is some random value.
    > > This is later deferenced and the system crashes after accessing some
    > > invalid address.
    > >
    > > This patch hacks powerpc to allocate per-cpu areas for node IDs that
    > > have no corresponding CPU id. This gets around the immediate problem but
    > > it should be discussed if there is a requirement for a DEFINE_PER_NODE
    > > and how it should be implemented.
    > >
    > > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
    > > ---
    > > arch/powerpc/kernel/setup_64.c | 20 ++++++++++++++++++++
    > > 1 files changed, 20 insertions(+), 0 deletions(-)
    > >
    > > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
    > > index 1f68160..a5f52d4 100644
    > > --- a/arch/powerpc/kernel/setup_64.c
    > > +++ b/arch/powerpc/kernel/setup_64.c
    > > @@ -588,6 +588,26 @@ void __init setup_per_cpu_areas(void)
    > > paca[i].data_offset = ptr - __per_cpu_start;
    > > memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
    > > }
    > > +#ifdef CONFIG_SLQB
    > > + /*
    > > + * SLQB abuses DEFINE_PER_CPU to setup a per-node area. This trick
    > > + * assumes that ever node ID will have a CPU of that ID to match.
    > > + * On systems with memoryless nodes, this may not hold true. Hence,
    > > + * we take a second pass initialising a "per-cpu" area for node-ids
    > > + * that SLQB can use
    > > + */
    >
    > Very trivial, but there's a little trailing whitespace in the first line
    > of the comment (checkpatch warns on it.) You also spelled initializing
    > wrong.

    re: spelling. Not really. Think internationally.

    ---
    ~Randy
    LPC 2009, Sept. 23-25, Portland, Oregon
    http://linuxplumbersconf.org/2009/


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