On 2014/8/18 9:13, tangchen wrote:
> Hi tj,
>
> On 08/17/2014 07:08 PM, Tejun Heo wrote:
>> Hello,
>>
>> On Sat, Aug 16, 2014 at 10:36:41PM +0800, Xishi Qiu wrote:
>>> numa_clear_node_hotplug()? There is only numa_clear_kernel_node_hotplug().
>> Yeah, that one.
>>
>>> If we don't clear hotpluggable flag in free_low_memory_core_early(), the
>>> memory which marked hotpluggable flag will not free to buddy allocator.
>>> Because __next_mem_range() will skip them.
>>>
>>> free_low_memory_core_early
>>> for_each_free_mem_range
>>> for_each_mem_range
>>> __next_mem_range
>> Ah, okay, so the patch fixes __next_mem_range() and thus makes
>> free_low_memory_core_early() to skip hotpluggable regions unlike
>> before. Please explain things like that in the changelog. Also,
>> what's its relationship with numa_clear_kernel_node_hotplug()? Do we
>> still need them? If so, what are the different roles that these two
>> separate places serve?
>
> numa_clear_kernel_node_hotplug() only clears hotplug flags for the nodes
> the kernel resides in, not for hotpluggable nodes. The reason why we did
> this is to enable the kernel to allocate memory in case all the nodes are
> hotpluggable.
>
Hi TangChen,
I find a problem in numa_init() (arch/x86/mm/numa.c)
numa_init()
...
ret = init_func(); // this will mark hotpluggable flag from SRAT
...
memblock_set_bottom_up(false);
...
ret = numa_register_memblks(&numa_meminfo); // this will alloc node data(pglist_data)
...
numa_clear_kernel_node_hotplug(); // in case all the nodes are hotpluggable
...
If all the nodes are marked hotpluggable flag, alloc node data will fail.
Because __next_mem_range_rev() will skip the hotpluggable memory regions.
numa_register_memblks()
setup_node_data()
memblock_find_in_range_node()
__memblock_find_range_top_down()
for_each_mem_range_rev()
__next_mem_range_rev()
What do you think?
How about move numa_clear_kernel_node_hotplug() into numa_register_memblks(),
like this:
numa_register_memblks()
...
memblock_set_node(mb->start, mb->end - mb->start,
&memblock.reserved, mb->nid);
}
+ numa_clear_kernel_node_hotplug();
/*
* If sections array is gonna be used for pfn -> nid mapping, check
...
Thanks,
Xishi Qiu
> And we clear hotplug flags for all the nodes in free_low_memory_core_early()
> is because if we do not, all hotpluggable memory won't be able to be freed
> to buddy after Qiu's patch.
>
> Thanks.
>
>
> .
>
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