makedumpfile: get_max_mapnr() from ELF header problem

[Michael Holzheu]

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.

Hello Atsushi,

If you don't like that solution, what about using the mem_map_data[]
array of makedumpfile to adjust "max_mapnr"?

The patch below also works fine for my dump.

Michael
---
 makedumpfile.c |   14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -2829,7 +2829,8 @@ get_mem_map_without_mm(void)
 int
 get_mem_map(void)
 {
-	int ret;
+	unsigned long max_pfn = 0;
+	int ret, i;
 
 	switch (get_mem_type()) {
 	case SPARSEMEM:
@@ -2861,6 +2862,17 @@ get_mem_map(void)
 		ret = FALSE;
 		break;
 	}
+	/*
+	 * Adjust "max_mapnr" for the case that Linux uses less memory
+	 * than is dumped. For example when "mem=" has been used for the
+	 * dumped system.
+	 */
+	for (i = 0; i < info->num_mem_map; i++) {
+		if (info->mem_map_data[i].mem_map == NOT_MEMMAP_ADDR)
+			continue;
+		max_pfn = MAX(max_pfn, info->mem_map_data[i].pfn_end);
+	}
+	info->max_mapnr = max_pfn;
 	return ret;
 }