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

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Date:   Wed, 22 Apr 2020 16:55:19 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Laura Abbott <labbott@...hat.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>,
        Eric Biederman <ebiederm@...ssion.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 03/10] mm/migrate: separate PageHighMem() and
 PageHighMemZone() use case

2020년 4월 22일 (수) 오후 4:44, Christoph Hellwig <hch@...radead.org>님이 작성:
>
> On Mon, Apr 20, 2020 at 04:59:35PM +0900, js1304@...il.com wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> > 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@....com>
> > ---
> >  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.