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    SubjectRe: [PATCH 1/5] x86: Change size of node ids from u8 to u16 fixup
    On Jan 19, 2008 4:41 PM, Mike Travis <travis@sgi.com> wrote:
    > David Rientjes wrote:
    > > On Sat, 19 Jan 2008, Mike Travis wrote:
    > >
    > >>> Yeah, NID_INVAL is negative so no unsigned type will work here,
    > >>> unfortunately. And that reduces the intended savings of your change since
    > >>> the smaller type can only be used with a smaller CONFIG_NODES_SHIFT.
    > >>>
    > >> Excuse my ignorance but why wouldn't this work:
    > >>
    > >> static numanode_t pxm_to_node_map[MAX_PXM_DOMAINS]
    > >> = { [0 ... MAX_PXM_DOMAINS - 1] = NUMA_NO_NODE };
    > >> ...
    > >>>> int acpi_map_pxm_to_node(int pxm)
    > >>>> {
    > >>> int node = pxm_to_node_map[pxm];
    > >>>
    > >>> if (node < 0)
    > >> numanode_t node = pxm_to_node_map[pxm];
    > >>
    > >
    > > Because NUMA_NO_NODE is 0xff on x86. That's a valid node id for
    > > configurations with CONFIG_NODES_SHIFT equal to or greater than 8.
    >
    > Perhaps numanode_t should be set to u16 if MAX_NUMNODES > 255 to
    > allow for an invalid value of 255?
    >
    > #if MAX_NUMNODES > 255
    > typedef u16 numanode_t;
    > #else
    > typedef u8 numanode_t;
    > #endif
    >
    > >
    > >> if (node != NUMA_NO_NODE) {
    > >
    > > Wrong, this should be
    > >
    > > node == NUMA_NO_NODE
    >
    > Oops, yes you're right.
    >
    >
    > >>>> if (nodes_weight(nodes_found_map) >= MAX_NUMNODES)
    > >>>> return NID_INVAL;
    > >>>> node = first_unset_node(nodes_found_map);
    > >>>> __acpi_map_pxm_to_node(pxm, node);
    > >>>> node_set(node, nodes_found_map);
    > >>>> }
    > >
    > > The net result of this is that if a proximity domain is looked up through
    > > acpi_map_pxm_to_node() and already has a mapping to node 255 (legal with
    > > CONFIG_NODES_SHIFT == 8), this function will return NID_INVAL since the
    > > weight of nodes_found_map is equal to MAX_NUMNODES.
    >
    > >
    > > You simply can't use valid node id's to signify invalid or unused node
    > > ids.
    > >
    > >> or change:
    > >> #define NID_INVAL (-1)
    > >> to
    > >> #define NID_INVAL ((numanode_t)(-1))
    > >> ...
    > >> if (node != NID_INVAL) {
    > >
    > > You mean
    > >
    > > node == NID_INVAL
    > >
    > >>>> if (nodes_weight(nodes_found_map) >= MAX_NUMNODES)
    > >>>> return NID_INVAL;
    > >>>> node = first_unset_node(nodes_found_map);
    > >>>> __acpi_map_pxm_to_node(pxm, node);
    > >>>> node_set(node, nodes_found_map);
    > >>>> }
    > >
    > > That's the equivalent of your NUMA_NO_NODE code above. The fact remains
    > > that (numanode_t)-1 is still a valid node id for MAX_NUMNODES >= 256.
    > >
    > > So, as I said in my initial reply, the only way to get the savings you're
    > > looking for is to use u8 for CONFIG_NODES_SHIFT <= 7 and then convert all
    > > NID_INVAL users to use NUMA_NO_NODE.
    >
    > Yes, I agree. I'll do the changes you're suggesting.
    >
    > > Additionally, Linux has always discouraged typedefs when they do not
    > > define an architecture-specific size. The savings from your patch for
    > > CONFIG_NODES_SHIFT == 7 would be 256 bytes for this mapping.
    > >
    > > It's simply not worth it.
    >
    > So are you saying that I should just use u16 for all node ids whether
    > CONFIG_NODES_SHIFT > 7 or not? Othersise, I would think that defining a
    > typedef is a fairly clean solution.
    >
    > A quick grep shows that there are 35 arrays defined by MAX_NUMNODES in
    > x86_64, 38 in X86_32 (not verified.) So it's not exactly a trivial
    > amount of memory.

    just use int for node id, and -1 will be NON_VALID...
    or s16?

    YH


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