Re: [PATCH 02/16] selftests/mm: add folio-order check for VA ranges

> is_backed_by_folio() answers "what order folio backs this page", but
> mTHP collapse tests need the range-level question: is every
> order-aligned window of this VA range backed by one folio of exactly

Nit:                          ^ address (even without Virtual) reads
better to me here and in the subject.

> that order, mapped head-to-tail?
> 
> Add is_range_backed_by_folio_orders(): per window, require a present
> and naturally aligned head PFN, a contiguous PFN run across the
> window, and is_backed_by_folio() agreeing on the order. A window
> assembled from pieces of different folios, or mapping a folio outside
> its natural position, fails the check.

I'd need claude to understand this one ;-P

> Assisted-by: Claude-Code:claude-opus-5
> Signed-off-by: Kiryl Shutsemau (Meta) <[email protected]>
>
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 343a15e25a9f..793342095420 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -365,6 +365,52 @@ bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
>  	return false;
>  }
>  
> +/*
> + * Check whether the range [start, start + len) is backed by folios of
> + * exactly @order, mapped at their natural alignment.
> + *
> + * is_backed_by_folio() classifies the folio backing one page; here we
> + * additionally require that each order-aligned window of the range maps

I don't think the description should be incremental on top of
is_backed_by_folio() 

> + * one such folio head-to-tail: the VA range must be naturally aligned,

Please spell out VA or just use "address". selftests are userspace,
"virtual" is kinda implied.

-- 
Sincerely yours,
Mike.