On Tue, 13 Jul 2010 13:11:14 +0900 Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > On Tue, Jul 13, 2010 at 12:19 PM, KAMEZAWA Hiroyuki > <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > On Tue, 13 Jul 2010 00:53:48 +0900 > > Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > > > >> Kukjin, Could you test below patch? > >> I don't have any sparsemem system. Sorry. > >> > >> -- CUT DOWN 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. > >> So in above case, pfn on 0x25000000 can pass pfn_valid's validation check. > >> It's not what we want. > >> > >> The Following patch adds check valid pfn range check on pfn_valid of sparsemem. > >> > >> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx> > >> Reported-by: Kukjin Kim <kgene.kim@xxxxxxxxxxx> > >> > >> P.S) > >> It is just RFC. If we agree with this, I will make the patch on mmotm. > >> > >> -- > >> > >> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > >> index b4d109e..6c2147a 100644 > >> --- a/include/linux/mmzone.h > >> +++ b/include/linux/mmzone.h > >> @@ -979,6 +979,8 @@ struct mem_section { > >> struct page_cgroup *page_cgroup; > >> unsigned long pad; > >> #endif > >> + unsigned long start_pfn; > >> + unsigned long end_pfn; > >> }; > >> > > > > I have 2 concerns. > > 1. This makes mem_section twice. Wasting too much memory and not good for cache. > > But yes, you can put this under some CONFIG which has small number of mem_section[]. > > > > I think memory usage isn't a big deal. but for cache, we can move > fields into just after section_mem_map. > I don't think so. This addtional field can eat up the amount of memory you saved by unmap. > > 2. This can't be help for a case where a section has multiple small holes. > > I agree. But this(not punched hole but not filled section problem) > isn't such case. But it would be better to handle it altogether. :) > > > > > Then, my proposal for HOLES_IN_MEMMAP sparsemem is below. > > == > > Some architectures unmap memmap[] for memory holes even with SPARSEMEM. > > To handle that, pfn_valid() should check there are really memmap or not. > > For that purpose, __get_user() can be used. > > Look at free_unused_memmap. We don't unmap pte of hole memmap. > Is __get_use effective, still? > __get_user() works with TLB and page table, the vaddr is really mapped or not. If you got SEGV, __get_user() returns -EFAULT. It works per page granule. Thanks, -Kame -- 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>