Re: [PATCH v4 05/13] mm/arch: Provide pud_pfn() fallback

[Jason Gunthorpe]

On Tue, Apr 02, 2024 at 06:43:56PM -0400, Peter Xu wrote:

> I actually tested this without hitting the issue (even though I didn't
> mention it in the cover letter..).  I re-kicked the build test, it turns
> out my "make alldefconfig" on loongarch will generate a config with both
> HUGETLB=n && THP=n, while arch/loongarch/configs/loongson3_defconfig has
> THP=y (which I assume was the one above build used).  I didn't further
> check how "make alldefconfig" generated the config; a bit surprising that
> it didn't fetch from there.

I suspect it is weird compiler variations.. Maybe something is not
being inlined.

> (and it also surprises me that this BUILD_BUG can trigger.. I used to try
>  triggering it elsewhere but failed..)

As the pud_leaf() == FALSE should result in the BUILD_BUG never being
called and the optimizer removing it.

Perhaps the issue is that the pud_leaf() is too far from the pud_pfn?

Jason