On Mon, Jul 12, 2010 at 11:45:41AM +0100, Russell King - ARM Linux wrote: > On Mon, Jul 12, 2010 at 06:52:28PM +0900, Minchan Kim wrote: > > Hello. > > > > On Mon, Jul 12, 2010 at 5:32 PM, Kukjin Kim <kgene.kim@xxxxxxxxxxx> wrote: > > > Russell, > > > > > > Hi, > > > > > > Kukjin Kim wrote: > > >> Russell wrote: > > >> > So, memory starts at 0x20000000 and finishes at 0x25000000. That's > > > fine. > > >> > That doesn't mean the section size is 16MB. > > >> > > > >> > As I've already said, the section size has _nothing_ what so ever to do > > >> > with the size of memory, or the granularity of the size of memory. By > > >> > way of illustration, it is perfectly legal to have a section size of > > >> > 256MB but only have 1MB in a section and this is perfectly legal. So > > >> > sections do not have to be completely filled. > > >> > > > >> Actually, as you know, the hole's area of mem_map is freed from bootmem if > > > a > > >> section has a hole when initializing sparse memory. > > >> > > >> I identified that a section doesn't need to be a contiguous area of > > > physical > > >> memory when reading your comment with the fact that the mem_map of a > > > section > > >> can be smaller than the size of a section. > > >> > > >> I found, however, the kernel panics when modifying min_free_kbytes file in > > >> the proc filesystem if a section has a hole. > > >> > > >> While processing the change of min_free_kbytes in the kernel, page > > >> descriptors in a hole of an online section is accessed. > > > > > > As I said, following error happens. > > > It would be helpful to me if any opinions or comments. > > > > > > > Could you test below patch? > > Also, you should select ARCH_HAS_HOLES_MEMORYMODEL in your config. > > But hang on. Where are the hole(s)? > > The DRAM setup is: > 0x20000000-0x25000000, 0x40000000-0x50000000, 0x50000000-0x58000000 > > which with SECTION_SIZE_BITS set to 28 gives three sections of memory, > and each sparsemem section does not have a hole. > > No zone should cross a sparsemem section boundary. > > Moreover, our pfn_valid() now returns false for any and all invalid PFNs. True if it isn't sparsemem. But look at pfn_valid in sparsemem. It just checks that there is a section and section_mem_map has SECTION_HAS_MEM_MAP. The first section in above case has just 80M memory but section has 256M. So, 0x25000000 - 28000000 is the hole. If you pass pfn whihc is 0x2500000, let's see pfn_valid. 1. We pass pfn_to_section_nr check 2. Both __nr_to_section and valid_section is vaild. static inline int pfn_valid(unsigned long pfn) { if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS) return 0; return valid_section(__nr_to_section(pfn_to_section_nr(pfn))); } What prevent above hole's case? I think at least pfn_valid in sparsemem need bank range check like pfn_valid of ARM in FLATMEM. -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html