On Wed, Apr 7, 2010 at 12:48 AM, Venkatram Tummala <venkatram867@xxxxxxxxx> wrote: > I completely agree with you. I was just trying to clarify Xianghua's > statement "last 128 MB is used for HIGHMEM". I got the feeling that he > thought that last 128MB can be used for vmalloc, IO and for HIGHMEM. So, i > was clarifying that last 128MB is not "used for highmem" but it is used to > support highmem.(among many other things). That was what i intended. > > On Tue, Apr 6, 2010 at 7:09 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: >> >> On 04/06/2010 07:04 PM, Venkatram Tummala wrote: >> > Hey Xiao, >> > >> > last 128MB is not used for highmem. last 128MB is used for data >> > structures(page tables etc.) to support highmem . Highmem is not >> > something which is "INSIDE" Kernel's Virtual Address space. Highmem >> > refers to a region of "Physical memory" which can be mapped into >> > kernel's virtual address space through page tables. >> > >> > Regards, >> > Venkatram Tummala >> > >> >> Not quite. >> >> The vmalloc region is for *anything which is dynamically mapped*, which >> includes I/O, vmalloc, and HIGHMEM (kmap). >> >> -hpa >> >> -- >> H. Peter Anvin, Intel Open Source Technology Center >> I work for Intel. I don't speak on their behalf. >> > > Thanks Venkatram, do these sound right: 1. All HIGHMEM(physical address beyond 896MB) are kmapped back into the last 128MB kernel "virtual" address space(using page tables stored in the last 128MB physical address). That also implies it's a very limited virtual space for large memory system and need do kunmap when you're done with it(so you can kmap other physical memories in). I'm not familiar with large-memory systems, not sure how kmap cope with that using this limited 128M window assuming kernel is 1:3 split. 2. The last 128MB physical address can be used for page tables(kmap), vmalloc, IO,etc Regards, Xianghua -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
