On Wed, Apr 7, 2010 at 5:40 PM, Xianghua Xiao <[email protected]>wrote:
> On Wed, Apr 7, 2010 at 12:48 AM, Venkatram Tummala > <[email protected]> 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 <[email protected]> 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. > Small correction here, page-table is not store in last 128MB of physical memory. Instead the complete page table for 4GB virtual address space is stored in kernel data-structures (kernel data section). ~cnanda 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 [email protected] > Please read the FAQ at http://kernelnewbies.org/FAQ > >
