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. > 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? -- 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