Re: [PATCH] x86: numa: setup_node_data(): drop dead code and rename function

[Luiz Capitulino <lcapitulino@redhat.com>]

On Mon, 30 Jun 2014 16:42:39 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> On Thu, 19 Jun 2014, Luiz Capitulino wrote:
> 
> > The setup_node_data() function allocates a pg_data_t object, inserts it
> > into the node_data[] array and initializes the following fields:
> > node_id, node_start_pfn and node_spanned_pages.
> > 
> > However, a few function calls later during the kernel boot,
> > free_area_init_node() re-initializes those fields, possibly with
> > different values. This means that the initialization done by
> > setup_node_data() is not used.
> > 
> > This causes a small glitch when running Linux as a hyperv numa guest:
> > 
> > [    0.000000] SRAT: PXM 0 -> APIC 0x00 -> Node 0
> > [    0.000000] SRAT: PXM 0 -> APIC 0x01 -> Node 0
> > [    0.000000] SRAT: PXM 1 -> APIC 0x02 -> Node 1
> > [    0.000000] SRAT: PXM 1 -> APIC 0x03 -> Node 1
> > [    0.000000] SRAT: Node 0 PXM 0 [mem 0x00000000-0x7fffffff]
> > [    0.000000] SRAT: Node 1 PXM 1 [mem 0x80200000-0xf7ffffff]
> > [    0.000000] SRAT: Node 1 PXM 1 [mem 0x100000000-0x1081fffff]
> > [    0.000000] NUMA: Node 1 [mem 0x80200000-0xf7ffffff] + [mem 0x100000000-0x1081fffff] -> [mem 0x80200000-0x1081fffff]
> > [    0.000000] Initmem setup node 0 [mem 0x00000000-0x7fffffff]
> > [    0.000000]   NODE_DATA [mem 0x7ffec000-0x7ffeffff]
> > [    0.000000] Initmem setup node 1 [mem 0x80800000-0x1081fffff]
> > [    0.000000]   NODE_DATA [mem 0x1081fa000-0x1081fdfff]
> > [    0.000000] crashkernel: memory value expected
> > [    0.000000]  [ffffea0000000000-ffffea0001ffffff] PMD -> [ffff88007de00000-ffff88007fdfffff] on node 0
> > [    0.000000]  [ffffea0002000000-ffffea00043fffff] PMD -> [ffff880105600000-ffff8801077fffff] on node 1
> > [    0.000000] Zone ranges:
> > [    0.000000]   DMA      [mem 0x00001000-0x00ffffff]
> > [    0.000000]   DMA32    [mem 0x01000000-0xffffffff]
> > [    0.000000]   Normal   [mem 0x100000000-0x1081fffff]
> > [    0.000000] Movable zone start for each node
> > [    0.000000] Early memory node ranges
> > [    0.000000]   node   0: [mem 0x00001000-0x0009efff]
> > [    0.000000]   node   0: [mem 0x00100000-0x7ffeffff]
> > [    0.000000]   node   1: [mem 0x80200000-0xf7ffffff]
> > [    0.000000]   node   1: [mem 0x100000000-0x1081fffff]
> > [    0.000000] On node 0 totalpages: 524174
> > [    0.000000]   DMA zone: 64 pages used for memmap
> > [    0.000000]   DMA zone: 21 pages reserved
> > [    0.000000]   DMA zone: 3998 pages, LIFO batch:0
> > [    0.000000]   DMA32 zone: 8128 pages used for memmap
> > [    0.000000]   DMA32 zone: 520176 pages, LIFO batch:31
> > [    0.000000] On node 1 totalpages: 524288
> > [    0.000000]   DMA32 zone: 7672 pages used for memmap
> > [    0.000000]   DMA32 zone: 491008 pages, LIFO batch:31
> > [    0.000000]   Normal zone: 520 pages used for memmap
> > [    0.000000]   Normal zone: 33280 pages, LIFO batch:7
> > 
> > In this dmesg, the SRAT table reports that the memory range for node 1
> > starts at 0x80200000. However, the line starting with "Initmem" reports
> > that node 1 memory range starts at 0x80800000. The "Initmem" line is
> > reported by setup_node_data() and is wrong, because the kernel ends up
> > using the range as reported in the SRAT table.
> > 
> > This commit drops all that dead code from setup_node_data(), renames it
> > to alloc_node_data() and adds a printk() to free_area_init_node() so
> > that we report a node's memory range accurately.
> > 
> > Here's the same dmesg section with this patch applied:
> > 
> > [    0.000000] SRAT: PXM 0 -> APIC 0x00 -> Node 0
> > [    0.000000] SRAT: PXM 0 -> APIC 0x01 -> Node 0
> > [    0.000000] SRAT: PXM 1 -> APIC 0x02 -> Node 1
> > [    0.000000] SRAT: PXM 1 -> APIC 0x03 -> Node 1
> > [    0.000000] SRAT: Node 0 PXM 0 [mem 0x00000000-0x7fffffff]
> > [    0.000000] SRAT: Node 1 PXM 1 [mem 0x80200000-0xf7ffffff]
> > [    0.000000] SRAT: Node 1 PXM 1 [mem 0x100000000-0x1081fffff]
> > [    0.000000] NUMA: Node 1 [mem 0x80200000-0xf7ffffff] + [mem 0x100000000-0x1081fffff] -> [mem 0x80200000-0x1081fffff]
> > [    0.000000] NODE_DATA(0) allocated [mem 0x7ffec000-0x7ffeffff]
> > [    0.000000] NODE_DATA(1) allocated [mem 0x1081fa000-0x1081fdfff]
> > [    0.000000] crashkernel: memory value expected
> > [    0.000000]  [ffffea0000000000-ffffea0001ffffff] PMD -> [ffff88007de00000-ffff88007fdfffff] on node 0
> > [    0.000000]  [ffffea0002000000-ffffea00043fffff] PMD -> [ffff880105600000-ffff8801077fffff] on node 1
> > [    0.000000] Zone ranges:
> > [    0.000000]   DMA      [mem 0x00001000-0x00ffffff]
> > [    0.000000]   DMA32    [mem 0x01000000-0xffffffff]
> > [    0.000000]   Normal   [mem 0x100000000-0x1081fffff]
> > [    0.000000] Movable zone start for each node
> > [    0.000000] Early memory node ranges
> > [    0.000000]   node   0: [mem 0x00001000-0x0009efff]
> > [    0.000000]   node   0: [mem 0x00100000-0x7ffeffff]
> > [    0.000000]   node   1: [mem 0x80200000-0xf7ffffff]
> > [    0.000000]   node   1: [mem 0x100000000-0x1081fffff]
> > [    0.000000] Node 0 memory range 0x00001000-0x7ffeffff
> > [    0.000000] On node 0 totalpages: 524174
> > [    0.000000]   DMA zone: 64 pages used for memmap
> > [    0.000000]   DMA zone: 21 pages reserved
> > [    0.000000]   DMA zone: 3998 pages, LIFO batch:0
> > [    0.000000]   DMA32 zone: 8128 pages used for memmap
> > [    0.000000]   DMA32 zone: 520176 pages, LIFO batch:31
> > [    0.000000] Node 1 memory range 0x80200000-0x1081fffff
> > [    0.000000] On node 1 totalpages: 524288
> > [    0.000000]   DMA32 zone: 7672 pages used for memmap
> > [    0.000000]   DMA32 zone: 491008 pages, LIFO batch:31
> > [    0.000000]   Normal zone: 520 pages used for memmap
> > [    0.000000]   Normal zone: 33280 pages, LIFO batch:7
> > 
> > This commit was tested on a two node bare-metal NUMA machine and Linux
> > as a numa guest on hyperv and qemu/kvm.
> > 
> > PS: The wrong memory range reported by setup_node_data() seems to be
> >     harmless in the current kernel because it's just not used. However,
> >     that bad range is used in kernel 2.6.32 to initialize the old boot
> >     memory allocator, which causes a crash during boot.
> > 
> > Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> 
> With this patch, the dmesg changes break one of my scripts that we use to 
> determine the start and end address of a node (doubly bad because there's 
> no sysfs interface to determine this otherwise and we have to do this at 
> boot to acquire the system topology).
> 
> Specifically, the removal of the
> 
> 	"Initmem setup node X [mem 0xstart-0xend]"
> 
> lines that are replaced when each node is onlined to
> 
> 	"Node 0 memory range 0xstart-0xend"
> 
> And if I just noticed this breakage when booting the latest -mm kernel, 
> I'm assuming I'm not the only person who is going to run into it.  Is it 
> possible to not change the dmesg output?

Sure. I can add back the original text. The only detail is that with this
patch that line is now printed a little bit later during boot and the
NODA_DATA lines also changed. Are you OK with that?

What's the guidelines on changing what's printed in dmesg?

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