Hi,

On my ARM machine, the total kernel memory is not aligned to the section
size SECTION_SIZE_BITS.

I observe kernel crashes in the following 3 scenarios:
i)    When we do a "cat /proc/pagetypeinfo": This happens because the
pfn_valid() macro is not able to detect invalid PFNs in the loop in

vmstat.c: pagetypeinfo_showblockcount_print().
ii)    When we do "echo xxxx > /proc/vm/sys/min_free_kbytes": This happens
because the pfn_valid() macro is not able to detect invalid PFNs in

                                    page_alloc.c:
setup_zone_migrate_reserve().
iii)   When I try to copy a really huge file form one directory to another:
This happens because the CONFIG_HOLES_IN_ZONE config option is not set.

                                                So,
the code in move_freepages() crashes.

I did find one patch somewhat related to this problem at:
https://patchwork.kernel.org/patch/793862/
However, this patch is not suitable for my version of linux-2.6.35.13
because this uses memblock_*() functionality and
CONFIG_HAVE_MEMBLOCK is not enabled for my platform. Also, I am not sure
whether this will solve point iii) above, as pfn_valid_within()
will continue to return 1 back to the caller when it should be calling
pfn_vald() instead.

I created a solution patch for this and would appreciate it if anyone in
these mailing lists could review this patch and tell me whether:
i)  There is a better way to do this or,
ii)  There is already a more suitable patch for the configuration I am
mentioning above.

Patch:

--- linux-2.6.35.11.p29-FR/arch/arm/Kconfig 2011-07-27 10:27:02.243936001
+0530

+++ linux-2.6.35.11.p29-FR.new/arch/arm/Kconfig 2011-07-27
09:54:00.823935866 +0530

@@ -581,6 +581,16 @@ config OABI_COMPAT

config ARCH_HAS_HOLES_MEMORYMODEL

bool

+config ARCH_HAS_PFN_VALID

+ bool

+ depends on SPARSEMEM

+ default y

+

+config HOLES_IN_ZONE

+ bool

+ depends on SPARSEMEM

+ default y

+

# Discontigmem is deprecated

config ARCH_DISCONTIGMEM_ENABLE

bool

--- linux-2.6.35.9/arch/arm/mm/init.c 2011-06-13 15:18:47.921796999 +0530

+++ linux-2.6.35.9.new/arch/arm/mm/init.c 2011-06-13 11:59:47.236796983
+0530

@@ -350,6 +350,27 @@ static void arm_memory_present(struct me

{

}

#else

+#ifdef CONFIG_ARCH_HAS_PFN_VALID

+int arch_pfn_valid(unsigned long pfn)

+{

+ struct meminfo *mi = &meminfo;

+ unsigned int left = 0, right = mi->nr_banks;

+

+ do {

+ unsigned int mid = (right + left) / 2;

+ struct membank *bank = &mi->bank[mid];

+

+ if (pfn < bank_pfn_start(bank))

+ right = mid;

+ else if (pfn >= bank_pfn_end(bank))

+ left = mid + 1;

+ else

+ return 1;

+ } while (left < right);

+ return 0;

+}

+#endif

+

static void arm_memory_present(struct meminfo *mi, int node)

{

int i;

--- linux-2.6.35.9/include/linux/mmzone.h 2010-11-23 00:31:26.000000000
+0530

+++ linux-2.6.35.9.new/include/linux/mmzone.h 2011-06-13 12:32:37.182796701
+0530

@@ -1062,10 +1062,20 @@ static inline struct mem_section *__pfn_

return __nr_to_section(pfn_to_section_nr(pfn));

}

+#ifdef CONFIG_ARCH_HAS_PFN_VALID

+int arch_pfn_valid(unsigned long) ;

+#endif

+

static inline int pfn_valid(unsigned long pfn)

{

if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)

return 0;

+

+#ifdef CONFIG_ARCH_HAS_PFN_VALID

+ if (!arch_pfn_valid(pfn))

+ return 0 ;

+#endif

+

return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));

}

@@ -1073,6 +1083,12 @@ static inline int pfn_present(unsigned l

{

if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)

return 0;

+

+#ifdef CONFIG_ARCH_HAS_PFN_VALID

+ if (!arch_pfn_valid(pfn))

+ return 0 ;

+#endif

+

return present_section(__nr_to_section(pfn_to_section_nr(pfn)));

}


Thanks,
Kautuk.