Re: [PATCH] mm: vmpressure: scale window size based on machine memory

[David Hildenbrand (Arm)]

On 9/1/26 08:43, Taha Sezer wrote:
> Hi Lorenzo, Andrew,
> 
> Thanks for the honest and thorough review.
> 
> Lorenzo -- yes, I did use an AI coding assistant (Claude) to help
> write this patch. I should have included an Assisted-by: tag from
> the start and I apologise for the omission. That was a mistake on
> my part, not an attempt to hide anything -- I simply was not aware of
> the disclosure process for my first submission.
> 
> Andrew -- you are absolutely right about the math. The original window
> is SWAP_CLUSTER_MAX * 16 = 512 pages, and my formula clamp(fls(mem),
> 4, 64) produces values well below 16 for every machine under ~8 TB.
> The patch shrinks the window on virtually all real hardware, which is
> the exact opposite of what the commit message promises. Embarrassing,
> and I should have caught this before sending.
> 
> For a bit of context on why I chose mm/: I have been writing a hobby
> kernel from scratch (Caelum) that includes a VMM with COW and demand
> paging, a slab allocator with NUMA-aware allocation, TLB shootdown
> via IPI, and SMP boot -- so memory management is the area I am most
> comfortable with. That said, comfortable with the concepts clearly
> did not save me from a basic arithmetic mistake here, and I take full
> responsibility for not verifying the output carefully enough.
> 
> Before I send a v2, I would appreciate any guidance:
> 
>   1. Is the general idea still worth pursuing -- scaling the window
>      logarithmically with total RAM using fls(), or do you think
>      the fixed 512-page window is fine as-is and this TODO is
>      better left alone?
> 
>   2. If the approach is worth fixing: would keeping the original
>      multiplier of 16 as the floor (so the window only ever grows
>      beyond 512 pages) be the right direction, or would you prefer
>      a different scaling strategy entirely?
> 
>   3. Any other advice for a first-time contributor on how to
>      approach mm/ patches more carefully?
> 
> I will hold off on v2 until I hear back, so I do not waste anyone's
> time with another half-baked attempt. The next version will include
> a proper Assisted-by: Claude:claude-opus-4 tag.

Note that we now prefer

Assisted-by: LLM

-- 
Cheers,

David