Re: [LSF/MM/BPF TOPIC] KSM Enhancements: Selective KSM

[David Hildenbrand <david@redhat.com>]

On 01.02.25 03:15, Sourav Panda wrote:
> Hi,

Hi,

> 
> 
> KSM is a powerful tool for deduplicating memory, reducing usage by merging
> 
> identical pages across processes. However, there are certain interface and
> 
> implementation aspect that prevents its deployment in our use case; wherein
> 
> security and efficiency (CPU overhead - due to background scanning) are of
> 
> greater importance.
> 
> 
> We propose Selective KSM, a mechanism to control when the merging takes
> 
> place and what pages can be merged together. We do this by partitioning the
> 
> merge-space as per security-domains and carryout the merging as part of a
> 
> synchronous syscall. Doing so, we ensure sensitive-content is not merged
> 
> with non-sensitive content.

I'll note that there was an RFC for uKSM [1] last year. Unfortunately, I 
didn't have time to look into it in more detail, and there was never any 
push for it.

In particular, it proposed an interface:

- /proc/uksm/merge enables the merging of two pages given their process
   IDs and addresses.
- /proc/uksm/unmerge allows unmerging a previously merged KSM page.
- /proc/uksm/cmp provides a lightweight mechanism to check page content
   equivalence before invoking a merge operation.

[1] 
https://lore.kernel.org/linux-mm/20240329104035.62942-1-teawater@antgroup.com/T/

-- 
Cheers,

David / dhildenb