Re: [RFC v11 08/14] mm: page_frag: some minor refactoring before adding new API

[Alexander H Duyck]

On Wed, 2024-07-31 at 20:35 +0800, Yunsheng Lin wrote:
> On 2024/7/30 23:12, Alexander H Duyck wrote:
> 
> ...
> 
> > >         }
> > > 
> > >         nc->pagecnt_bias--;
> > >         nc->remaining = remaining - fragsz;
> > > 
> > >         return encoded_page_address(encoded_va) +
> > >                 (page_frag_cache_page_size(encoded_va) - remaining);
> > 
> > Parenthesis here shouldn't be needed, addition and subtractions
> > operations can happen in any order with the result coming out the same.
> 
> I am playing safe to avoid overflow here, as I am not sure if the allocator
> will give us the last page. For example, '0xfffffffffffff000 + 0x1000' will
> have a overflow.

So what if it does though? When you subtract remaining it will
underflow and go back to the correct value shouldn't it?