Messages in this thread | | | Date | Mon, 30 Apr 2007 00:17:55 -0700 | From | Andrew Morton <> | Subject | Re: CONFIG_HIGHMEM4G and 1GB RAM |
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On Sat, 28 Apr 2007 21:26:42 +0100 "Bradley Chapman" <kakadu@gmail.com> wrote:
> After installing a second 512MB SODIMM into my laptop, I noticed that > my 2.6.18.3 kernel only detected and used 896MB of the resulting 1GB, > and informed me that I needed to enable high memory in order to access > the remaining 127MB. > > While doing so, I noticed that the help text stated that enabling high > memory (in my case, CONFIG_HIGHMEM4G) should only be done if the > system the kernel is running on has more than 1GB, but less than 4GB - > it said that systems with 1GB should leave it off, which resulted in > an eighth of the installed memory going missing. A bit more research > found a three year old thread on this list where it was stated that > enabling CONFIG_HIGHMEM4G sometimes slows the system down due to > sometimes undesirable changes to the way the kernel sets up the memory > map. > > Basically, all I want to know is whether or not enabling > CONFIG_HIGHMEM4G for a laptop that has exactly 1GB of RAM will result > in any performance degradation. >
I would expect the advantages of the additional 128MB to considerably outweigh the cost of turning on CONFIG_HIGHMEM4G.
That cost will be a little extra CPU consumption inside the kernel, but the great majority of CPU consumption usually happens in userspace anyway.
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