Re: [PATCH net-next v3 3/3] page_pool: fix IOMMU crash when driver has already unbound

[Yunsheng Lin]

On 2024/11/12 22:19, Jesper Dangaard Brouer wrote:
>>
>> Yes, there seems to be many MM system internals, like the CONFIG_SPARSEMEM*
>> config, memory offline/online and other MM specific optimization that it
>> is hard to tell it is feasible.
>>
>> It would be good if MM experts can clarify on this.
>>
> 
> Yes, please.  Can Alex Duyck or MM-experts point me at some code walking
> entire system page table?
> 
> Then I'll write some kernel code (maybe module) that I can benchmark how
> long it takes on my machine with 384GiB. I do like Alex'es suggestion,
> but I want to assess the overhead of doing this on modern hardware.
> 

After looking more closely into MM subsystem, it seems there is some existing
pattern or API to walk the entire pages from the buddy allocator subsystem,
see the kmemleak_scan() in mm/kmemleak.c:
https://elixir.bootlin.com/linux/v6.12/source/mm/kmemleak.c#L1680

I used that to walk the pages in a arm64 system with over 300GB memory,
it took about 1.3 sec to do the walking, which seems acceptable?