Re: [RFC PATCH v2 2/3] mm: Add PUD level pagetable account

[Baolin Wang]

On 6/23/2022 9:28 PM, Matthew Wilcox wrote:
> On Wed, Jun 22, 2022 at 09:38:30AM -0500, Mike Rapoport wrote:
> > On Wed, Jun 22, 2022 at 04:58:53PM +0800, Baolin Wang wrote:
> > > +++ b/arch/loongarch/include/asm/pgalloc.h
> > > @@ -89,10 +89,15 @@ static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
> > >   static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long address)
> > >   {
> > >   	pud_t *pud;
> > > +	struct page *pg;
> >
> > 	struct page *page;
> >
> > looks better IMO.
> >
> > > +
> > > +	pg = alloc_pages(GFP_KERNEL & ~__GFP_HIGHMEM, PUD_ORDER);
>
> GFP_KERNEL does not include __GFP_HIGHMEM, so you can just use
> GFP_KERNEL here.

Yes. Thanks.

> > > +	if (!pg)
> > > +		return NULL;
> > >   
> > > -	pud = (pud_t *) __get_free_pages(GFP_KERNEL, PUD_ORDER);
> > > -	if (pud)
> > > -		pud_init((unsigned long)pud, (unsigned long)invalid_pmd_table);
> > > +	pgtable_set_and_inc(pg);
> > > +	pud = (pud_t *)page_address(pg);
> >
> > I don't think __get_free_pages() should be replaced with alloc_pages()
> > here, just call pgtable_set_and_inc() with virt_to_page(pud).
>
> I don't understand why you want that.  Take a look at the implementation
> of __get_free_pages().  Converting back to a struct page after calling
> that seems like a real waste of time to me.

IMO I have no strong preference. The code can be simpler with using 
__get_free_pages(), however like Matthew said it will add more conversion.