On Sun, Jul 18, 2010 at 07:18:31PM +0900, Minchan Kim wrote: > 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. > First off, thanks for working on this. > 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. > > We can match section size to smallest valid size.(ex, above case, 16M) > But Russell doesn't like it due to mem_section's memory overhead with different > configuration(ex, 512K section). > > I tried to add valid pfn range in mem_section but everyone doesn't like it > due to size overhead. Also IIRC, it was vunerable to a hole being punched in the middle of the section. > This patch is suggested by KAMEZAWA-san. > I just fixed compile error and change some naming. > > This patch registers address of mem_section to memmap itself's page struct's > pg->private field. This means the page is used for memmap of the section. > Otherwise, the page is used for other purpose and memmap has a hole. > > This patch is based on mmotm-2010-07-01-12-19. > > Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Reported-by: Kukjin Kim <kgene.kim@xxxxxxxxxxx> > --- > arch/arm/mm/init.c | 9 ++++++++- > include/linux/mmzone.h | 21 ++++++++++++++++++++- > mm/Kconfig | 5 +++++ > mm/sparse.c | 41 +++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 74 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c > index cfe4c5e..4586f40 100644 > --- a/arch/arm/mm/init.c > +++ b/arch/arm/mm/init.c > @@ -234,6 +234,11 @@ static void __init arm_bootmem_free(struct meminfo *mi) > arch_adjust_zones(zone_size, zhole_size); > > free_area_init_node(0, zone_size, min, zhole_size); > + > + for_each_bank(i, mi) { > + mark_memmap_hole(bank_pfn_start(&mi->bank[i]), > + bank_pfn_end(&mi->bank[i]), true); > + } > } Why do we need to mark banks both valid and invalid? Is it not enough to just mark the holes in free_memmap() and assume it is valid otherwise? > > #ifndef CONFIG_SPARSEMEM > @@ -386,8 +391,10 @@ free_memmap(unsigned long start_pfn, unsigned long end_pfn) > * If there are free pages between these, > * free the section of the memmap array. > */ > - if (pg < pgend) > + if (pg < pgend) { > + mark_memmap_hole(pg >> PAGE_SHIFT, pgend >> PAGE_SHIFT, false); > free_bootmem(pg, pgend - pg); > + } > } > > /* > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 9ed9c45..2ed9728 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -15,6 +15,7 @@ > #include <linux/seqlock.h> > #include <linux/nodemask.h> > #include <linux/pageblock-flags.h> > +#include <linux/mm_types.h> > #include <generated/bounds.h> > #include <asm/atomic.h> > #include <asm/page.h> > @@ -1047,11 +1048,29 @@ static inline struct mem_section *__pfn_to_section(unsigned long pfn) > return __nr_to_section(pfn_to_section_nr(pfn)); > } > > +void mark_memmap_hole(unsigned long start, unsigned long end, bool valid); > + The naming is confusing with the "valid" parameter. What's a "valid hole"? I can see that one being a cause of head scratching in the future :) > +#ifdef CONFIG_SPARSEMEM_HAS_HOLE Why not use CONFIG_ARCH_HAS_HOLES_MEMORYMODEL ? > +static inline int page_valid(struct mem_section *ms, unsigned long pfn) > +{ > + struct page *page = pfn_to_page(pfn); > + struct page *__pg = virt_to_page(page); > + return __pg->private == (unsigned long)ms; > +} > +#else > +static inline int page_valid(struct mem_section *ms, unsigned long pfn) > +{ > + return 1; > +} > +#endif > + > static inline int pfn_valid(unsigned long pfn) > { > + struct mem_section *ms; > if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS) > return 0; > - return valid_section(__nr_to_section(pfn_to_section_nr(pfn))); > + ms = __nr_to_section(pfn_to_section_nr(pfn)); > + return valid_section(ms) && page_valid(ms, pfn); > } So it appears here that we unconditionally check page_valid() but we know which sections had holes in them at the time we called mark_memmap_hole(). Can the sections with holes be tagged so that only some sections need to call page_valid()? As it is, ARM will be taking a an performance hit just in case the section has holes but it should only need to take a performance hit on the corner case where a section is not fully populated. > > static inline int pfn_present(unsigned long pfn) > diff --git a/mm/Kconfig b/mm/Kconfig > index 527136b..959ac1d 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -128,6 +128,11 @@ config SPARSEMEM_VMEMMAP > pfn_to_page and page_to_pfn operations. This is the most > efficient option when sufficient kernel resources are available. > > +config SPARSEMEM_HAS_HOLE > + bool "allow holes in sparsemem's memmap" > + depends on ARM && SPARSEMEM && !SPARSEMEM_VMEMMAP > + default n > + > # eventually, we can have this option just 'select SPARSEMEM' > config MEMORY_HOTPLUG > bool "Allow for memory hot-add" > diff --git a/mm/sparse.c b/mm/sparse.c > index 95ac219..76d5012 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -615,6 +615,47 @@ void __init sparse_init(void) > free_bootmem(__pa(usemap_map), size); > } > > +#ifdef CONFIG_SPARSEMEM_HAS_HOLE > +/* > + * Fill memmap's pg->private with a pointer to mem_section. > + * pfn_valid() will check this later. (see include/linux/mmzone.h) > + * Evenry arch should call > + * mark_memmap_hole(start, end, true) # for all allocated mem_map > + * and, after that, > + * mark_memmap_hole(start, end, false) # for all holes in mem_map. > + * please see usage in ARM. > + */ > +void mark_memmap_hole(unsigned long start, unsigned long end, bool valid) > +{ > + struct mem_section *ms; > + unsigned long pos, next; > + struct page *pg; > + void *memmap, *mapend; > + > + for (pos = start; pos < end; pos = next) { > + next = (pos + PAGES_PER_SECTION) & PAGE_SECTION_MASK; > + ms = __pfn_to_section(pos); > + if (!valid_section(ms)) > + continue; > + > + for (memmap = (void*)pfn_to_page(pos), > + /* The last page in section */ > + mapend = pfn_to_page(next-1); > + memmap < mapend; memmap += PAGE_SIZE) { > + pg = virt_to_page(memmap); > + if (valid) > + pg->private = (unsigned long)ms; > + else > + pg->private = 0; > + } > + } > +} > +#else > +void mark_memmap_hole(unsigned long start, unsigned long end, bool valid) > +{ > +} > +#endif > + The patch should also delete memmap_valid_within() and replace it with a call to pfn_valid_within(). The reason memmap_valid_within() existed was because sparsemem had holes punched in it but I'd rather not see use of that function grow. > #ifdef CONFIG_MEMORY_HOTPLUG > #ifdef CONFIG_SPARSEMEM_VMEMMAP > static inline struct page *kmalloc_section_memmap(unsigned long pnum, int nid, > -- > 1.7.0.5 > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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>