linux-kernel - Re: [PATCH v2 00/10] change the implementation of the PageHighMem()

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Date:   Fri, 1 May 2020 21:15:30 +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 00/10] change the implementation of the PageHighMem()

2020년 5월 1일 (금) 오후 7:55, Christoph Hellwig <hch@...radead.org>님이 작성:
>
> On Fri, May 01, 2020 at 07:52:35PM +0900, Joonsoo Kim wrote:
> > > - New code will pop up which gets it wrong and nobody will notice for
> > >   a long time.
> >
> > Hmm... I think that it's not that hard to decide correct macro. If we rename
> > PageHighMem() with PageDirectMapped(), they, PageDirectMapped() and
> > PageHighMemZone(), are self-explanation macro. There would be no
> > confusion to use.
>
> What confuses me is why we even need PageHighMemZone - mostly code
> should not care about particular zones.  Maybe just open coding
> PageHighMemZone makes more sense - it is a little more cumersome, but
> at least it makes it explicit what we check for.  I already sent you
> an incremental diff for one obvious place, but maybe we need to look
> through the remaining ones if we can kill them or open code them in an
> obvious way.

I think that PageHighMemZone() is long and complicated enough to have
a macro.

PageHighMemZone(page) = is_highmem_idx(zone_idx(page_zone(page))

Instead of open-code, how about changing the style of macro like as
page_from_highmem()? What PageHighMemZone() represent is derivated
attribute from the page so PageXXX() style may not be appropriate.

Thanks.