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Message-ID: <20200501122655.GC21897@infradead.org>
Date: Fri, 1 May 2020 05:26:55 -0700
From: Christoph Hellwig <hch@...radead.org>
To: js1304@...il.com
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
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,
Christoph Hellwig <hch@...radead.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 06/10] mm/hugetlb: separate PageHighMem() and
PageHighMemZone() use case
On Wed, Apr 29, 2020 at 12:26:39PM +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>
Why do we care about the zone here? This only cares about having
kernel direct mapped pages as far as I can tell.
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