Re: [PATCH] mm/hugetlb: fix surplus pages in dissolve_free_huge_page()

[Jinjiang Tu <tujinjiang@huawei.com>]

在 2025/3/3 19:16, Jinjiang Tu 写道:
>
> 在 2025/3/3 18:25, David Hildenbrand 写道:
>> On 03.03.25 07:09, Jinjiang Tu wrote:
>>> In dissolve_free_huge_page(), free huge pages are dissolved without
>>> adjusting surplus count. However, free huge pages may be accounted as
>>> surplus pages, and will lead to wrong surplus count.
>>>
>>> Steps to reproduce:
>>> 1) create 64 huge pages for node1
>>> 2) run a program to reserve (don't consume) all the huge pages
>>> 3) echo 0 > nr_huge_pages for node1. After this step, free huge 
>>> pages in
>>> Node1 are surplus.
>>> 4) create 80 huge pages for node0
>>> 5) offline memory of node1 and kill the program in step 2)
>>
>> Can you elaborate the "offline memory" part? How much are you 
>> offlining (the complete node vs a single memory block?)
> I reproduce this issue on qemu. The memory onlining and offlining 
> operations are:
>
> 1）Node1 is memory-less at first. Hot-add memory to node1 by executing 
> the two commands in qemu monitor
> object_add memory-backend-ram,id=mem1,size=1G
> device_add pc-dimm,id=dimm1,memdev=mem1,node=1
>
> 2）online one memory block of Node1 with：
> echo online_movable > /sys/devices/system/node/node1/memoryX/state
>
> 3) offline the memory block of Node1 with：
> echo offline > /sys/devices/system/node/node1/memoryX/state
The memory range to offline contains the free surplus huge pages created 
in step1) ~ step3)
>>
>> If I skip the offlining part, it all works as expected on a 6.12 kernel.
>>