Re: [LSF/MM/BPF TOPIC] Improve KSM for code patching use-cases

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2025-01-28 10:22, Mathieu Desnoyers wrote:
> Hi,
> 
> I submit this topic proposal for your consideration:
> 
> We are implementing a code patching library which essentially
> reimplements static keys for userspace. (work in progress,
> not released yet)
> 
> One of the problems we face when patching code from libraries
> and executables from nops to jumps is Copy-on-Write (CoW), which
> increases memory use and prevents sharing code pages across
> processes.
> 
> I suspect we can improve Kernel Samepage Merging (KSM) to
> better handle scenarios where pages which are the result of
> a CoW from a given file/offset are modified shortly after
> their CoW, and then are stable for most of their lifetime.
> 
> This would allow merging CoW pages when the resulting
> modification makes them identical again. This could be
> achieved by tracking possible duplicates on a per
> file/offset basis, which should be more efficient than
> a global scan.
> 
> I would like to discuss this topic with Filesystem and MM
> experts to get their input.

Here are the slides I presented during my talk:

https://drive.google.com/file/d/18EkWsvILbPlTDRHI22sHIWUhlqBsYILy/view?usp=sharing


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com