On Tue, Jul 13, 2010 at 1:23 PM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > 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. Agree. > >> > 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. I mean following as. For example, there is a struct page in on 0x20000000. int pfn_valid_mapped(unsigned long pfn) { struct page *page = pfn_to_page(pfn); /* hole page is 0x2000000 */ char *lastbyte = (char *)(page+1)-1; /* lastbyte is 0x2000001f */ char byte; /* We pass this test since free_unused_memmap doesn't unmap pte */ if(__get_user(byte, page) != 0) return 0; /* * (0x20000000 & PAGE_MASK) == (0x2000001f & PAGE_MASK) * So, return 1, it is wrong result. */ if ((((unsigned long)page) & PAGE_MASK) == (((unsigned long)lastbyte) & PAGE_MASK)) return 1; return (__get_user(byte,lastbyte) == 0); } Am I missing something? -- 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