Messages in this thread | | | Date | Tue, 06 Apr 2010 16:32:00 -0700 | From | "H. Peter Anvin" <> | Subject | Re: why choose 896MB to the start point of ZONE_HIGHMEM |
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On 04/06/2010 04:27 PM, Youngwhan Song wrote: > Nice explanation, Venkatram, > > Just one question pop up mind. > > What if actual physical memory is only 256MB? How does kernel divide > virtual memory? Do we need to specify the region to kernel? Or will > kernel itself decide it automatically? >
If there is less than 896 MB of physical memory, the vmalloc region is automatically extended (in your case, it will be 768 MB in size.) There will be no HIGHMEM in such a case, and if you are compiling your own kernel you will gain considerable speed by disabling HIGHMEM support completely.
This, of course, was the norm back when Linux was first created, and a typical amount of memory was 8 MB or so. That we'd have gigabytes of memory seemed very distant at the time.
-hpa
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