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Date: Mon, 4 May 2020 12:10:36 +0900 From: Joonsoo Kim <js1304@...il.com> To: "Eric W. Biederman" <ebiederm@...ssion.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>, Christian Koenig <christian.koenig@....com>, Huang Rui <ray.huang@....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 03/10] kexec: separate PageHighMem() and PageHighMemZone() use case 2020년 5월 1일 (금) 오후 11:06, Eric W. Biederman <ebiederm@...ssion.com>님이 작성: > > js1304@...il.com writes: > > > 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. > > Hmm. > > What happened to the notion of deprecating and reducing the usage of > highmem? I know that we have some embedded architectures where it is > still important but this feels like it flies in the face of that. AFAIK, deprecating highmem requires some more time and, before then, we need to support it. > > This part of kexec would be much more maintainable if it had a proper > mm layer helper that tested to see if the page matched the passed in > gfp flags. That way the mm layer could keep changing and doing weird > gyrations and this code would not care. Good idea! I will do it. > > What would be really helpful is if there was a straight forward way to > allocate memory whose physical address fits in the native word size. > > > All I know for certain about this patch is that it takes a piece of code > that looked like it made sense, and transfroms it into something I can > not easily verify, and can not maintain. Although I decide to make a helper as you described above, I don't understand why you think that a new code isn't maintainable. It is just the same thing with different name. Could you elaborate more why do you think so? Thanks.
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