Re: [PATCH v2] mm: allow deferred page init for vmemmap only

From: Pavel Tatashin
Date: Fri May 11 2018 - 10:18:42 EST

> Thanks that helped me to see the problem. On the other hand isn't this a
> bit of an overkill? AFAICS this affects only NEED_PER_CPU_KM which is !SMP
> and DEFERRED_STRUCT_PAGE_INIT makes only very limited sense on UP,
> right?

> Or do we have more such places?

I do not know other places, but my worry is that trap_init() is arch
specific and we cannot guarantee that arches won't do virt to phys in
trap_init() in other places. Therefore, I think a proper fix is simply
allow DEFERRED_STRUCT_PAGE_INIT when it is safe to do virt to phys without
accessing struct pages, which is with SPARSEMEM_VMEMMAP.