Re: [FYI] DAMON and virtio-balloon in DeepSeek's DSec paper

[Jialiang Huang <huang-jl@deepseek.com>]

>> Muchun's vmemmap work is also interesting to us. My understanding is
>> that it allocates private backing for struct page metadata on demand,
>> which could help reduce the upfront memory overhead for large images.
>
> Although I haven't had a chance and time to look into that, the main
> concern from me is that mmap() access will call
> "dax_fault_iter->vmemmap_materialize_page()", and malicious sandbox
> workloads (or not malicious, just valid mmap workloads) can cause guest
> memory OOMs due to "struct page balloon" for large rootfs in the worst
> cases and cause the follow-up mmap access failure, because the guest
> memory size may not even fulfill "struct page" for large rootfs.
>
> Thanks,
> Gao Xiang

Agreed, if a workload actually accesses a sufficiently large range of the
image, allocating struct page metadata on demand could indeed exhaust
guest memory.

Best,
Jialiang Huang