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Message-ID: <4BBC1807.1090004@zytor.com> Date: Tue, 06 Apr 2010 22:28:39 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Chetan Nanda <chetannanda@...il.com> CC: Venkatram Tummala <venkatram867@...il.com>, Joel Fernandes <agnel.joel@...il.com>, Frank Hu <frank.hu.2001@...il.com>, hayfeng Lee <teklife.kernel@...il.com>, linux-kernel@...r.kernel.org, linux-kernel@...kernel.org, kernelnewbies@...linux.org Subject: Re: why choose 896MB to the start point of ZONE_HIGHMEM On 04/06/2010 09:05 PM, Chetan Nanda wrote: > > I have a question here, what if I have a 32bit system with 2GB of RAM, > so in that case my 896MB - 2GB RAM would be in accessible? > What my understanding on the subject is: > Only 896 MB of physical RAM is directly mapped on to kernel 1G virtual > address space. And we still require page table settings to do that (page > table would be identity mapping). But for rest of RAM, i.e. whenever > there is need to access physical RAM beyond 896MB then that page will be > mapped on to pages from 128MB kernel virtual address space (1GB - 896MB > = 128MB), and AFAIK kmap is just for that. > > Please correct me if i am wrong > Correct. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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