Re: [PATCH 03/10] mm/migrate: separate PageHighMem() and PageHighMemZone() use case

[Joonsoo Kim]

2020ë 4ì 22ì (ì) ìí 4:44, Christoph Hellwig <hch@xxxxxxxxxxxxx>ëì ìì:
>
> On Mon, Apr 20, 2020 at 04:59:35PM +0900, js1304@xxxxxxxxx wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> >
> > Until now, PageHighMem() is used for two different cases. One is to check
> > if there is a direct mapping for this page or not. The other is to check
> > the zone of this page, that is, weather it is the highmem type zone or not.
> >
> > Now, we have separate functions, PageHighMem() and PageHighMemZone() for
> > each cases. Use appropriate one.
> >
> > Note that there are some rules to determine the proper macro.
> >
> > 1. If PageHighMem() is called for checking if the direct mapping exists
> > or not, use PageHighMem().
> > 2. If PageHighMem() is used to predict the previous gfp_flags for
> > this page, use PageHighMemZone(). The zone of the page is related to
> > the gfp_flags.
> > 3. If purpose of calling PageHighMem() is to count highmem page and
> > to interact with the system by using this count, use PageHighMemZone().
> > This counter is usually used to calculate the available memory for an
> > kernel allocation and pages on the highmem zone cannot be available
> > for an kernel allocation.
> > 4. Otherwise, use PageHighMemZone(). It's safe since it's implementation
> > is just copy of the previous PageHighMem() implementation and won't
> > be changed.
> >
> > I apply the rule #2 for this patch.
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > ---
> >  include/linux/migrate.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> > index 3e546cb..9a57766 100644
> > --- a/include/linux/migrate.h
> > +++ b/include/linux/migrate.h
> > @@ -47,7 +47,7 @@ static inline struct page *new_page_nodemask(struct page *page,
> >               order = HPAGE_PMD_ORDER;
> >       }
> >
> > -     if (PageHighMem(page) || (zone_idx(page_zone(page)) == ZONE_MOVABLE))
> > +     if (PageHighMemZone(page) || zone_idx(page_zone(page)) == ZONE_MOVABLE)
> >               gfp_mask |= __GFP_HIGHMEM;
>
> I think this would be much cleaner if you open coded PageHighMemZone
> here.
>
> E.g.
>
>         int zone = page_zone(page);
>
>         if (is_highmem_idx(zone) || zone_idx(zone) == ZONE_MOVABLE)

Okay. I will use open code here to make two condition checks similar form.

Thanks.