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Date:   Mon, 4 May 2020 12:08:23 +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>, kernel-team@....com,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 07/10] mm: separate PageHighMem() and PageHighMemZone()
 use case

2020년 5월 1일 (금) 오후 9:30, Christoph Hellwig <hch@...radead.org>님이 작성:
>
> On Wed, Apr 29, 2020 at 12:26:40PM +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 #3 for this patch.
> >
> > Acked-by: Roman Gushchin <guro@...com>
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> > ---
> >  mm/memory_hotplug.c | 2 +-
> >  mm/page_alloc.c     | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 555137b..891c214 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -593,7 +593,7 @@ void generic_online_page(struct page *page, unsigned int order)
> >       __free_pages_core(page, order);
> >       totalram_pages_add(1UL << order);
> >  #ifdef CONFIG_HIGHMEM
> > -     if (PageHighMem(page))
> > +     if (PageHighMemZone(page))
> >               totalhigh_pages_add(1UL << order);
> >  #endif
> >  }
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index fc5919e..7fe5115 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7444,7 +7444,7 @@ void adjust_managed_page_count(struct page *page, long count)
> >       atomic_long_add(count, &page_zone(page)->managed_pages);
> >       totalram_pages_add(count);
> >  #ifdef CONFIG_HIGHMEM
> > -     if (PageHighMem(page))
> > +     if (PageHighMemZone(page))
> >               totalhigh_pages_add(count);
> >  #endif
>
> This function already uses the page_zone structure above, I think
> life would be easier of you compare against that, as that makes
> the code more obvious.

If I can kill all the PageHighMemZone() macro, I will use page_zone() above.
However, if it's not possible, I will leave it as it is. It would be
simpler than
your suggestion.

Thanks.

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