Re: [PATCH v2 1/2] mm/page_alloc: drop the unnecessary pfn_valid() for start pfn

[Baolin Wang]

On 4/24/2023 6:54 PM, Michal Hocko wrote:
> On Mon 24-04-23 18:46:40, Baolin Wang wrote:
> > On 4/24/2023 5:50 PM, Michal Hocko wrote:
> > > On Sun 23-04-23 18:59:10, Baolin Wang wrote:
> > > > We've already used pfn_to_online_page() for start pfn to make sure
> > >
> > > Who is we? I do not see any note explicitly requiring that start_pfn has
> > > to be valid for __pageblock_pfn_to_page.
> >
> > Sorry for confusing, what I mean is the __pageblock_pfn_to_page() function,
> > which has used pfn_to_online_page() for start pfn. So the pfn_valid() in
> > __pageblock_pfn_to_page() for start pfn is unnecessary.
> >
> > I will update the commit log to make it clear.
>
> Your comment suggested that the check _has_ already been done. Which is
> not the case. pfn_to_online_page is called later in the function so I
> guess you should rephrase as following:
>
> "
> __pageblock_pfn_to_page currently performs both pfn_valid check and
> pfn_to_online_page. The former one is redundant because the latter is a
> stronger check. Drop pfn_valid.
> "

Yes, will change the commit log.

> With that or something going along with that. Feel free to add
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks.

> > > > it is online and valid, so the pfn_valid() for the start pfn is
> > > > unnecessary, drop it.
> > > >
> > > > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > > > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
> > > > Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> > > > ---
> > > > Changes from v1:
> > > >    - Collect reviewed tags. Thanks David and Ying.
> > > > ---
> > > >    mm/page_alloc.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > > index 9de2a18519a1..6457b64fe562 100644
> > > > --- a/mm/page_alloc.c
> > > > +++ b/mm/page_alloc.c
> > > > @@ -1512,7 +1512,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
> > > >    	/* end_pfn is one past the range we are checking */
> > > >    	end_pfn--;
> > > > -	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
> > > > +	if (!pfn_valid(end_pfn))
> > > >    		return NULL;
> > > >    	start_page = pfn_to_online_page(start_pfn);
> > > > --
> > > > 2.27.0