2020년 5월 1일 (금) 오후 11:06, Eric W. Biederman <ebiederm@xxxxxxxxxxxx>님이 작성: > > js1304@xxxxxxxxx writes: > > > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > > > 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.
