Hi Matthew,
On Wed, 28 Dec 2022 22:36:20 +0000 Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> On Wed, Dec 28, 2022 at 07:34:08PM +0800, Kefeng Wang wrote:
> > +static inline struct page *damon_get_page(unsigned long pfn)
> > +{
> > + struct folio *folio = damon_get_folio(pfn);
> > +
> > + /* when folio is NULL, return &(0->page) mean return NULL */
> > + return &folio->page;
>
> I really don't think this comment is needed. This is the standard idiom
> for converting from a folio to its head page.
Well, I think some of DAMON code readers (at least me) might not yet that
familiar with Folio, as it has not been a while since DAMON started using
Folio. Also, maybe I overlooked some comments or documents, but I was unable
to sure if the offset of 'page' in 'folio' is intended to be never changed with
any future changes, or not. So I thought adding one more line of explanation
here could be helpful for someone.
I also show some code using 'folio_page(folio, 0)', so I might not be the only
one who at least sometimes forget the idiom. For helping people remember this
idiom easier, what do you think about having a new macro or static inline
function, say, 'folio_head_page()' and comment why passing NULL is ok on the
function? IMHO, that would be easier to read.
Thanks,
SJ
