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[]. 2. This can't be help for a case where a section has multiple small holes. 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. This idea is from ia64_pfn_valid(). Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> --- include/linux/mmzone.h | 12 ++++++++++++ mm/sparse.c | 17 +++++++++++++++++ 2 files changed, 29 insertions(+) Index: mmotm-2.6.35-0701/include/linux/mmzone.h =================================================================== --- mmotm-2.6.35-0701.orig/include/linux/mmzone.h +++ mmotm-2.6.35-0701/include/linux/mmzone.h @@ -1047,12 +1047,24 @@ static inline struct mem_section *__pfn_ return __nr_to_section(pfn_to_section_nr(pfn)); } +#ifndef CONFIG_ARCH_HAS_HOLES_IN_MEMMAP 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))); } +#else +extern int pfn_valid_mapped(unsigned long pfn); +static inline int pfn_valid(unsigned long pfn) +{ + if (pfn_to_seciton_nr(pfn) >= NR_MEM_SECTIONS) + return 0; + if (!valid_section(__nr_to_section(pfn_to_section_nr(pfn)))) + return 0; + return pfn_valid_mapped(pfn); +} +#endif static inline int pfn_present(unsigned long pfn) { Index: mmotm-2.6.35-0701/mm/sparse.c =================================================================== --- mmotm-2.6.35-0701.orig/mm/sparse.c +++ mmotm-2.6.35-0701/mm/sparse.c @@ -799,3 +799,20 @@ void sparse_remove_one_section(struct zo free_section_usemap(memmap, usemap); } #endif + +#ifdef CONFIG_ARCH_HAS_HOLES_IN_MEMMAP +int pfn_valid_mapped(unsigned long pfn) +{ + struct page *page = pfn_to_page(pfn); + char *lastbyte = (char *)(page+1)-1; + char byte; + + if(__get_user(byte, page) != 0) + return 0; + + if ((((unsigned long)page) & PAGE_MASK) == + (((unsigned long)lastbyte) & PAGE_MASK)) + return 1; + return (__get_user(byte,lastbyte) == 0); +} +#endif -- 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>