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    SubjectRe: [PATCH 7/7] Add /proc/sys/vm/compact_node for the explicit compaction of a node
    On Tue, 29 May 2007, Christoph Lameter wrote:

    > On Tue, 29 May 2007, Mel Gorman wrote:
    >
    >> + if (nodeid < 0)
    >> + return -EINVAL;
    >> +
    >> + pgdat = NODE_DATA(nodeid);
    >> + if (!pgdat || pgdat->node_id != nodeid)
    >> + return -EINVAL;
    >
    > You cannot pass an arbitrary number to node data since NODE_DATA may do a
    > simple array lookup.
    >
    > Check for node < nr_node_ids first.
    >

    Very good point. Will fix

    > pgdat->node_id != nodeid? Sounds like something you should BUG() on.
    >

    On non-NUMA, NODE_DATA(anything) returns contig_page_data. I was catching
    where the node ID's didn't match up because node 0 was always returned.
    Checking nr_node_ids is the correct way of doing this.

    It's not a BUG() if bad ID is passed in here because we're checking user
    input. By returning -EINVAL the proc writer knows something bad happened
    without making a big deal about it.

    > IA64's NODE_DATA is
    >
    > struct ia64_node_data {
    > short active_cpu_count;
    > short node;
    > struct pglist_data *pg_data_ptrs[MAX_NUMNODES];
    > };
    >
    > /*
    > * Given a node id, return a pointer to the pg_data_t for the node.
    > *
    > * NODE_DATA - should be used in all code not related to system
    > * initialization. It uses pernode data structures to minimize
    > * offnode memory references. However, these structure are not
    > * present during boot. This macro can be used once cpu_init
    > * completes.
    > */
    > #define NODE_DATA(nid) (local_node_data->pg_data_ptrs[nid])
    >
    > x86_64 also does
    >
    > #define NODE_DATA(nid) (node_data[nid])
    >

    All spot on. Will fix.

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab
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