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Subject[PATCH] Tight check of pfn_valid on sparsemem - v2
Date
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 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. 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@gmail.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reported-by: Kukjin Kim <kgene.kim@samsung.com>
---
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);
+ }
}

#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);
+
+#ifdef CONFIG_SPARSEMEM_HAS_HOLE
+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);
}

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
+
#ifdef CONFIG_MEMORY_HOTPLUG
#ifdef CONFIG_SPARSEMEM_VMEMMAP
static inline struct page *kmalloc_section_memmap(unsigned long pnum, int nid,
--
1.7.0.5


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