Re: [PATCH] LoongArch: Add sparse memory vmemmap support

[Arnd Bergmann <arnd@arndb.de>]

On Mon, Jun 20, 2022 at 12:24 PM Huacai Chen <chenhuacai@kernel.org> wrote:
> On Fri, Jun 17, 2022 at 11:42 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Fri, Jun 17, 2022 at 4:58 PM Huacai Chen <chenhuacai@loongson.cn> wrote:
> > >
> > > Add sparse memory vmemmap support for LoongArch. SPARSEMEM_VMEMMAP
> > > uses a virtually mapped memmap to optimise pfn_to_page and page_to_pfn
> > > operations. This is the most efficient option when sufficient kernel
> > > resources are available.
> >
> > I have not looked at this in detail, but from a high-level perspective, it
> > seems very similar to the corresponding code in arch/arm64 and arch/x86.
> >
> > Can you try to merge the three copies into a generic helper and add that
> > to mm/sparse-vmemmap.c? If this does not work, can you describe in the
> > changelog text why these have to be architecture specific?
>
> It is difficult to merge, because LoongArch needs to call pud_init(),
> pmd_init() and other similar things which are unnecessary on ARM64 and
> X86.

 I can see that this part of the code is the same as mips. What is the
initialization
 for? Can it be encapsulated in an architecture specific inline
function (for mips
and loongarch), with a generic version like this?

#ifndef pud_init_invalid
static inline void pud_init_invalid(void *) {}
#endif

       Arnd