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

[Matthew Wilcox <willy@infradead.org>]

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.

> > +	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.