On Wed, 19 Mar 2014 07:14:25 +0000
Atsushi Kumagai <kumagai-atsushi at mxc.nes.nec.co.jp> wrote:
> >Hello Atsushi,
> >
> >I debugged my problem a bit further and tried to implement
> >a function that gets the maximum page frame number from the
> >Linux kernel memory management structures.
> >
> >I am no memory management expert, so the following patch probably
> >is not complete, but at least for my setup it worked.
>
> The patch looks good for your case, but I don't think it's a proper
> approach for this problem.
>
> Now, I think this is a problem of get_mm_sparsemem() in makedumpfile.
> To say in more detail, the problem is "wrong calculating the address
> of unused mem_map".
>
> Looking at the log you sent, some addresses of mem_map corresponding
> to unused pages look invalid like below:
>
> mem_map (256)
> mem_map : 80000c0002018
> pfn_start : 1000000
> pfn_end : 1010000
> mem_map (257)
> mem_map : 800001840400000
> pfn_start : 1010000
> pfn_end : 1020000
> ...
> mem_map (544)
> mem_map : a82400012f14fffc
> pfn_start : 2200000
> pfn_end : 2210000
>
> ...(and more)
>
> However, makedumpfile should calculate such unused mem_map addresses
> as 0(NOT_MEMMAP_ADDR). Actually it works as expected at least in my
> environment(x86_64):
>
> ...
> mem_map (16)
> mem_map : 0
> pfn_start : 80000
> pfn_end : 88000
> mem_map (17)
> mem_map : 0
> pfn_start : 88000
> pfn_end : 90000
> ...
>
> makedumpfile get the address from mem_section.section_mem_map,
> it will be initialized with zero:
>
> [CONFIG_SPARSEMEM_EXTREAM]
> paging_init()
> sparse_memory_present_with_active_regions()
> memory_present()
> sparse_index_init()
> sparse_index_alloc() // allocate mem_section with kzalloc()
>
> makedumpfile assumes the value of unused mem_section will remain as 0,
> but I suspect this assumption may be broken in your environment.
>
Hello Atshushi,
I noticed that my last patch was not complete. It only checked the
mem_section[] array for zero entries. But as you noticed, we also
have to check the section array that we get from the mem_section
entries.
So I updated the patch.
Michael
---
makedumpfile.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -2690,11 +2690,14 @@ nr_to_section(unsigned long nr, unsigned
{
unsigned long addr;
- if (is_sparsemem_extreme())
+ if (is_sparsemem_extreme()) {
+ if (mem_sec[SECTION_NR_TO_ROOT(nr)] == 0)
+ return NOT_KV_ADDR;
addr = mem_sec[SECTION_NR_TO_ROOT(nr)] +
(nr & SECTION_ROOT_MASK()) * SIZE(mem_section);
- else
+ } else {
addr = SYMBOL(mem_section) + (nr * SIZE(mem_section));
+ }
if (!is_kvaddr(addr))
return NOT_KV_ADDR;
@@ -2778,10 +2781,19 @@ get_mm_sparsemem(void)
}
for (section_nr = 0; section_nr < num_section; section_nr++) {
section = nr_to_section(section_nr, mem_sec);
- mem_map = section_mem_map_addr(section);
- mem_map = sparse_decode_mem_map(mem_map, section_nr);
- if (!is_kvaddr(mem_map))
+ if (section == NOT_KV_ADDR) {
mem_map = NOT_MEMMAP_ADDR;
+ } else {
+ mem_map = section_mem_map_addr(section);
+ if (mem_map == 0) {
+ mem_map = NOT_MEMMAP_ADDR;
+ } else {
+ mem_map = sparse_decode_mem_map(mem_map,
+ section_nr);
+ if (!is_kvaddr(mem_map))
+ mem_map = NOT_MEMMAP_ADDR;
+ }
+ }
pfn_start = section_nr * PAGES_PER_SECTION();
pfn_end = pfn_start + PAGES_PER_SECTION();
if (info->max_mapnr < pfn_end)
