Re: [PATCHv2 02/14] mm/sparse: Check memmap alignment

[Kiryl Shutsemau]

On Mon, Dec 22, 2025 at 04:34:40PM +0800, Muchun Song wrote:
> 
> 
> On 2025/12/18 23:09, Kiryl Shutsemau wrote:
> > The upcoming changes in compound_head() require memmap to be naturally
> > aligned to the maximum folio size.
> > 
> > Add a warning if it is not.
> > 
> > A warning is sufficient as MAX_FOLIO_ORDER is very rarely used, so the
> > kernel is still likely to be functional if this strict check fails.
> 
> Different architectures default to 2 MB alignment (mainly to
> enable huge mappings), which only accommodates folios up to
> 128 MB. Yet 1 GB huge pages are still fairly common, so
> validating 16 GB (MAX_FOLIO_SIZE) alignment seems likely to
> miss the most frequent case.

I don't follow. 16 GB check is more strict that anything smaller.
How can it miss the most frequent case?

> I’m concerned that this might plant a hidden time bomb: it
> could detonate at any moment in later code, silently triggering
> memory corruption or similar failures. Therefore, I don’t
> think a WARNING is a good choice.

We can upgrade it BUG_ON(), but I want to understand your logic here
first.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov