[PATCH] Tight check of pfn_valid on sparsemem - v4

From: Minchan Kim
Date: Mon Jul 26 2010 - 11:47:10 EST

Changelog since v3
o fix my totally mistake in v3
o use set_page_private and page_private

Changelog since v2
o Change some function names
o Remove mark_memmap_hole in memmap bring up

I have a plan following as after this patch is acked.

1) expand pfn_valid to FALTMEM in ARM
I think we can enhance pfn_valid of FLATMEM in ARM.
Now it is doing binary search and it's expesive.
First of all, After we merge this patch, I expand it to FALTMEM of ARM.

2) remove memmap_valid_within
We can remove memmap_valid_within by strict pfn_valid's tight check.

3) Optimize hole check in sparsemem
In case of spasemem, we can optimize pfn_valid through defining new flag
like SECTION_HAS_HOLE of hole mem_section.

== CUT HERE ==

Kukjin reported oops happen while he change min_free_kbytes
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

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-2010-07-19

Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Reported-by: Kukjin Kim <kgene.kim@xxxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
arch/arm/mm/init.c | 9 +++++++++
include/linux/mmzone.h | 21 ++++++++++++++++++++-
mm/mmzone.c | 33 +++++++++++++++++++++++++++++++++
3 files changed, 62 insertions(+), 1 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index bc98d5d..18b255d 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -238,6 +238,15 @@ static void __init arm_bootmem_free(struct meminfo *mi, unsigned long min,
arch_adjust_zones(zone_size, zhole_size);

free_area_init_node(0, zone_size, min, zhole_size);
+ /*
+ * mark pages on mem_map with valid using pg->private.
+ * mem_map on hole will be freed free_memmap later.
+ */
+ for_each_bank(i, mi) {
+ mark_valid_memmap(bank_pfn_start(&mi->bank[i]),
+ bank_pfn_end(&mi->bank[i]));
+ }

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 6e6e626..3b4d16f 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>
@@ -1032,11 +1033,29 @@ static inline struct mem_section *__pfn_to_section(unsigned long pfn)
return __nr_to_section(pfn_to_section_nr(pfn));

+void mark_valid_memmap(unsigned long start, unsigned long end);
+static inline int memmap_valid(unsigned long pfn)
+ struct page *page = pfn_to_page(pfn);
+ struct page *__pg = virt_to_page(page);
+ return page_private(__pg) == (unsigned long)__pg;
+static inline int memmap_valid(unsigned long pfn)
+ return 1;
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) && memmap_valid(pfn);

static inline int pfn_present(unsigned long pfn)
diff --git a/mm/mmzone.c b/mm/mmzone.c
index f5b7d17..8c3cf57 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -86,4 +86,37 @@ int memmap_valid_within(unsigned long pfn,

return 1;
+ * Fill pg->private on valid mem_map with page itself.
+ * pfn_valid() will check this later. (see include/linux/mmzone.h)
+ * Every arch for supporting hole of mem_map should call
+ * mark_valid_memmap(start, end). please see usage in ARM.
+ */
+void mark_valid_memmap(unsigned long start, unsigned long end)
+ struct mem_section *ms;
+ unsigned long pos, next;
+ struct page *pg;
+ void *memmap, *mapend;
+ for (pos = start; pos < end; pos = next) {
+ 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);
+ set_page_private(pg, (unsigned long)pg);
+ }
+ }
+void mark_valid_memmap(unsigned long start, unsigned long end)

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