On Tue, Apr 02, 2024 at 07:53:20PM -0300, Jason Gunthorpe wrote: > 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.
Good point, for some reason loongarch defined pud_leaf() without defining pud_pfn(), which does look strange. #define pud_leaf(pud) ((pud_val(pud) & _PAGE_HUGE) != 0) But I noticed at least MIPS also does it.. Logically I think one arch should define either none of both. > > Perhaps the issue is that the pud_leaf() is too far from the pud_pfn? My understanding is follow_pud_mask() should completely get optimized and follow_huge_pud() will be dropped in the compiler output if pud_leaf()==false. Thanks, -- Peter Xu
