Re: [PATCH] mm/page_alloc: Use write_seqlock_irqsave() instead write_seqlock() + local_irq_save().

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2023-06-23 11:58:05 [+0200], To Michal Hocko wrote:
>                                    But first I'm going to use
> hotplug-mem to see how it works.

I boot qemu with "-m 4G,slots=4,maxmem=16G". 

| ~# free -h
|                total        used        free      shared  buff/cache   available
| Mem:           3,8Gi       221Mi       3,6Gi       520Ki        80Mi       3,6Gi
| Swap:             0B          0B          0B

Telling qemu to add memory:
| object_add memory-backend-ram,id=mem1,size=4G
| device_add pc-dimm,id=dimm1,memdev=mem1

I see in Linux:
| ~# free -h
|                total        used        free      shared  buff/cache   available
| Mem:           7,8Gi       345Mi       7,5Gi       516Ki        80Mi       7,5Gi
| Swap:             0B          0B          0B

memory arrived. Nothing in dmesg and my printk in __build_all_zonelists()
did not trigger either. Same after I removed memory with:
| device_del dimm1
| object_del mem1

it is gone:
| ~# free -h
|                total        used        free      shared  buff/cache   available
| Mem:           3,8Gi       232Mi       3,6Gi       516Ki        80Mi       3,6Gi
| Swap:             0B          0B          0B

nothing in dmesg. What did I do wrong not to enter
__build_all_zonelists()?

Sebastian