On 26.04.2022 12:59, Wei Chen wrote: > On 2022/4/26 17:02, Jan Beulich wrote: >> On 18.04.2022 11:07, Wei Chen wrote: >>> VIRTUAL_BUG_ON is an empty macro used in phys_to_nid. This >>> results in two lines of error-checking code in phys_to_nid >>> that is not actually working and causing two compilation >>> errors: >>> 1. error: "MAX_NUMNODES" undeclared (first use in this function). >>> This is because in the common header file, "MAX_NUMNODES" is >>> defined after the common header file includes the ARCH header >>> file, where phys_to_nid has attempted to use "MAX_NUMNODES". >>> This error was resolved when we moved the definition of >>> "MAX_NUMNODES" to x86 ARCH header file. And we reserve the >>> "MAX_NUMNODES" definition in common header file through a >>> conditional compilation for some architectures that don't >>> need to define "MAX_NUMNODES" in their ARCH header files. >> >> No, that's setting up a trap for someone else to fall into, especially >> with the #ifdef around the original definition. Afaict all you need to >> do is to move that #define ahead of the #include in xen/numa.h. Unlike >> functions, #define-s can reference not-yet-defined identifiers. >> > > I had tried it before. MAX_NUMNODES depends on NODE_SHIFT. But > NODE_SHIFT depends on the definition status in asm/numa.h. If I move > MAX_NUMNODES to before asm/numa.h, then I have to move NODES_SHIFT as > well. But this will break the original design. NODES_SHIFT in xen/numa.h > will always be defined before asm/numa.h. This will be a duplicated > definition error.
I'm afraid I don't follow. MAX_NUMNODES depends on NODES_SHIFT only as soon as some code actually uses MAX_NUMNODES. It does not require NODES_SHIFT to be defined up front. Of course with the current layout (phys_to_nid() living in an inline function in asm/numa.h) things won't build. But wasn't the plan to move phys_to_nid() to xen/numa.h as well? Otherwise I'd recommend to introduce a new header, say numa-defs.h, holding (for now) just NODES_SHIFT. Then you'd include asm/numa-defs.h first and asm/numa.h only after having defined MAX_NUMNODES. But splitting the header should only be a last resort if things can't be made work another way. > How about I move MAX_NUMNODES to arm and x86 asm/numa.h in this patch > at the same time? Because in one of following patches, MAX_NUMNODES and > phys_to_nid will be moved to xen/numa.h at the same time? > >>> 2. error: wrong type argument to unary exclamation mark. >>> This is because, the error-checking code contains !node_data[nid]. >>> But node_data is a data structure variable, it's not a pointer. >>> >>> So, in this patch, we use ASSERT instead of VIRTUAL_BUG_ON to >>> enable the two lines of error-checking code. And fix the left >>> compilation errors by replacing !node_data[nid] to >>> !node_data[nid].node_spanned_pages. >>> >>> Because when node_spanned_pages is 0, this node has no memory, >>> numa_scan_node will print warning message for such kind of nodes: >>> "Firmware Bug or mis-configured hardware?". >> >> This warning is bogus - nodes can have only processors. Therefore I'd >> like to ask that you don't use it for justification. And indeed you > > Yes, you're right, node can only has CPUs! I will remove it. > >> don't need to: phys_to_nid() is about translating an address. The >> input address can't be valid if it maps to a node with no memory. >> > > Can I understand your comment: > Any input address is invalid, when node_spanned_pages is zero, because > this node has no memory? It's getting close, but it's not exactly equivalent I think. A node with 0 bytes of memory might (at least in theory) have an entry in memnodemap[]. But finding a node ID for that address would still not mean that at least one byte of memory at that address is present on the given node, because the node covers 0 bytes. Jan
