On Thu, Jul 29, 2010 at 10:46:13AM -0500, Christoph Lameter wrote: > On Thu, 29 Jul 2010, Minchan Kim wrote: > > > On Wed, Jul 28, 2010 at 12:02:16PM -0500, Christoph Lameter wrote: > > > On Thu, 29 Jul 2010, Minchan Kim wrote: > > > > invalid memmap pages will be freed by free_memmap and will be used > > > > on any place. How do we make sure it has PG_reserved? > > > > > > Not present memmap pages make pfn_valid fail already since there is no > > > entry for the page table (vmemmap) or blocks are missing in the sparsemem > > > tables. > > > > > > > Maybe I don't understand your point. > > > > > > I thought we are worrying about holes in the memmap blocks containing page > > > structs. Some page structs point to valid pages and some are not. The > > > invalid page structs need to be marked consistently to allow the check. > > > > The thing is that memmap pages which contains struct page array on hole will be > > freed by free_memmap in ARM. Please loot at arch/arm/mm/init.c. > > And it will be used by page allocator as free pages. > > Arg thats the solution to the mystery. freememmap() is arm specific hack! > > Sparsemem allows you to properly handle holes already and then pfn_valid > will work correctly. > > Why are the ways to manage holes in the core not used by arm? I did use ARCH_HAS_HOLES_MEMORYMODEL. It is used by only ARM now. If you disable the config, it doesn't affect the core. > > sparsemem does a table lookup to determine valid and invalid sections of > the memmp. > The thing is valid section also have a invalid memmap. Maybe my description isn't enough. Please look at description and following URL. We already confirmed this problem. http://www.spinics.net/lists/arm-kernel/msg92918.html == CUT HERE == Kukjin reported oops happen while he change min_free_kbytes http://www.spinics.net/lists/arm-kernel/msg92894.html It happen by memory map on sparsemem. The system has a memory map following as. section 0 section 1 section 2 0x20000000-0x25000000, 0x40000000-0x50000000, 0x50000000-0x58000000 SECTION_SIZE_BITS 28(256M) It means section 0 is an incompletely filled section. Nontheless, current pfn_valid of sparsemem checks pfn loosely. It checks only mem_section's validation but ARM can free mem_map on hole to save memory space. So in above case, pfn on 0x25000000 can pass pfn_valid's validation check. It's not what we want. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>