linux-kernel - Re: [PATCH 02/10] drm/ttm: separate PageHighMem() and PageHighMemZone() use case

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Message-ID: <CAAmzW4MkKmAcFDHartRE6UK4W2SdZ519RP2UXYxCxzrvUWTzdw@mail.gmail.com>
Date:   Tue, 21 Apr 2020 15:49:15 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Christian König <christian.koenig@....com>
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>,
        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 02/10] drm/ttm: separate PageHighMem() and
 PageHighMemZone() use case

2020년 4월 20일 (월) 오후 5:42, Christian König <christian.koenig@....com>님이 작성:
>
> Am 20.04.20 um 09:59 schrieb js1304@...il.com:
> > 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 #4 for this patch.
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> Reviewed-by: Christian König <christian.koenig@....com> for the TTM
> changes, but I can't judge if the general approach makes sense or not.

Thanks for review!
General approach needs to get an agreement from more developers.

Thanks.