Re: [PATCH 1/1] mem-hotplug: Handle node hole when initializing numa_meminfo.

[Tang Chen <tangchen@cn.fujitsu.com>]

On 07/01/2015 02:25 PM, Xishi Qiu wrote:
> On 2015/7/1 11:16, Tang Chen wrote:
>
>> When parsing SRAT, all memory ranges are added into numa_meminfo.
>> In numa_init(), before entering numa_cleanup_meminfo(), all possible
>> memory ranges are in numa_meminfo. And numa_cleanup_meminfo() removes
>> all ranges over max_pfn or empty.
>>
>> But, this only works if the nodes are continuous. Let's have a look
>> at the following example:
>>
>> We have an SRAT like this:
>> SRAT: Node 0 PXM 0 [mem 0x00000000-0x5fffffff]
>> SRAT: Node 0 PXM 0 [mem 0x100000000-0x1ffffffffff]
>> SRAT: Node 1 PXM 1 [mem 0x20000000000-0x3ffffffffff]
>> SRAT: Node 4 PXM 2 [mem 0x40000000000-0x5ffffffffff] hotplug
>> SRAT: Node 5 PXM 3 [mem 0x60000000000-0x7ffffffffff] hotplug
>> SRAT: Node 2 PXM 4 [mem 0x80000000000-0x9ffffffffff] hotplug
>> SRAT: Node 3 PXM 5 [mem 0xa0000000000-0xbffffffffff] hotplug
>> SRAT: Node 6 PXM 6 [mem 0xc0000000000-0xdffffffffff] hotplug
>> SRAT: Node 7 PXM 7 [mem 0xe0000000000-0xfffffffffff] hotplug
>>
>> On boot, only node 0,1,2,3 exist.
>>
>> And the numa_meminfo will look like this:
>> numa_meminfo.nr_blks = 9
>> 1. on node 0: [0, 60000000]
>> 2. on node 0: [100000000, 20000000000]
>> 3. on node 1: [20000000000, 40000000000]
>> 4. on node 4: [40000000000, 60000000000]
>> 5. on node 5: [60000000000, 80000000000]
>> 6. on node 2: [80000000000, a0000000000]
>> 7. on node 3: [a0000000000, a0800000000]
>> 8. on node 6: [c0000000000, a0800000000]
>> 9. on node 7: [e0000000000, a0800000000]
>>
>> And numa_cleanup_meminfo() will merge 1 and 2, and remove 8,9 because
>> the end address is over max_pfn, which is a0800000000. But 4 and 5
>> are not removed because their end addresses are less then max_pfn.
>> But in fact, node 4 and 5 don't exist.
>>
>> In a word, numa_cleanup_meminfo() is not able to handle holes between nodes.
>>
>> Since memory ranges in node 4 and 5 are in numa_meminfo, in numa_register_memblks(),
>> node 4 and 5 will be mistakenly set to online.
>>
>> In this patch, we use memblock_overlaps_region() to check if ranges in
>> numa_meminfo overlap with ranges in memory_block. Since memory_block contains
>> all available memory at boot time, if they overlap, it means the ranges
>> exist. If not, then remove them from numa_meminfo.
>>
> Hi Tang Chen,
>
> What's the impact of this problem?
>
> Command "numactl --hard" will show an empty node(no cpu and no memory,
> but pgdat is created), right?

On my box, if I run lscpu, the output looks like this:

NUMA node0 CPU(s):     0-14,128-142
NUMA node1 CPU(s):     15-29,143-157
NUMA node2 CPU(s):
NUMA node3 CPU(s):
NUMA node4 CPU(s):     62-76,190-204
NUMA node5 CPU(s):     78-92,206-220

Node 2 and 3 are not exist, but they are online.

Thanks.

>
> Thanks,
> Xishi Qiu
>
>> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
>> ---
>>   arch/x86/mm/numa.c       | 6 ++++--
>>   include/linux/memblock.h | 2 ++
>>   mm/memblock.c            | 2 +-
>>   3 files changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
>> index 4053bb5..0c55cc5 100644
>> --- a/arch/x86/mm/numa.c
>> +++ b/arch/x86/mm/numa.c
>> @@ -246,8 +246,10 @@ int __init numa_cleanup_meminfo(struct numa_meminfo *mi)
>>   		bi->start = max(bi->start, low);
>>   		bi->end = min(bi->end, high);
>>   
>> -		/* and there's no empty block */
>> -		if (bi->start >= bi->end)
>> +		/* and there's no empty or non-exist block */
>> +		if (bi->start >= bi->end ||
>> +		    memblock_overlaps_region(&memblock.memory,
>> +			bi->start, bi->end - bi->start) == -1)
>>   			numa_remove_memblk_from(i--, mi);
>>   	}
>>   
>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>> index 0215ffd..3bf6cc1 100644
>> --- a/include/linux/memblock.h
>> +++ b/include/linux/memblock.h
>> @@ -77,6 +77,8 @@ int memblock_remove(phys_addr_t base, phys_addr_t size);
>>   int memblock_free(phys_addr_t base, phys_addr_t size);
>>   int memblock_reserve(phys_addr_t base, phys_addr_t size);
>>   void memblock_trim_memory(phys_addr_t align);
>> +long memblock_overlaps_region(struct memblock_type *type,
>> +			      phys_addr_t base, phys_addr_t size);
>>   int memblock_mark_hotplug(phys_addr_t base, phys_addr_t size);
>>   int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
>>   int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 1b444c7..55b5f9f 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -91,7 +91,7 @@ static unsigned long __init_memblock memblock_addrs_overlap(phys_addr_t base1, p
>>   	return ((base1 < (base2 + size2)) && (base2 < (base1 + size1)));
>>   }
>>   
>> -static long __init_memblock memblock_overlaps_region(struct memblock_type *type,
>> +long __init_memblock memblock_overlaps_region(struct memblock_type *type,
>>   					phys_addr_t base, phys_addr_t size)
>>   {
>>   	unsigned long i;
>
>
> .
>

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