Re: [PATCH 2/2] mm: Indicate pfmemalloc pages in compound_head

[Matthew Wilcox]

On Sat, Apr 17, 2021 at 09:13:45PM +0000, David Laight wrote:
> >  		struct {	/* page_pool used by netstack */
> > -			/**
> > -			 * @dma_addr: might require a 64-bit value on
> > -			 * 32-bit architectures.
> > -			 */
> > +			unsigned long pp_magic;
> > +			unsigned long xmi;
> > +			unsigned long _pp_mapping_pad;
> >  			unsigned long dma_addr[2];
> >  		};
> 
> You've deleted the comment.

Yes.  It no longer added any value.  You can see dma_addr now occupies
two words.

> I also think there should be a comment that dma_addr[0]
> must be aliased to ->index.

That's not a requirement.  Moving the pfmemalloc indicator is a
requirement so that we _can_ use index, but there's no requirement about
how index is used.