[Crash-utility] Re: Crash shows - Invalid Memory size
Sharyathi Nagesh wrote:
Hi
We encountered this problem with Crash showing invalid memory when ran
on live machine:
======================================
[root@venuslp11 ~]# free -m
total used free shared buffers cached
Mem: 2151 1594 557 0 583 795
^^^^^^
-/+ buffers/cache: 215 1935
Swap: 1983 0 1983
[root@venuslp11 ~]# cat /proc/ppc64/lparcfg | grep DesMem
DesMem=2304
^^^^^^
[root@venuslp11 ~]# rpm -q crash
crash-4.0-3.7
[root@venuslp11 ~]# crash
...
KERNEL: /usr/lib/debug/lib/modules/2.6.18-1.2732.el5/vmlinux
DUMPFILE: /dev/mem
CPUS: 2
DATE: Fri Oct 27 07:58:54 2006
UPTIME: 01:12:34
LOAD AVERAGE: 1.52, 1.05, 0.48
TASKS: 98
NODENAME: venuslp11.upt.austin.ibm.com
RELEASE: 2.6.18-1.2732.el5
VERSION: #1 SMP Tue Oct 17 18:24:27 EDT 2006
MACHINE: ppc64 (2301 Mhz)
MEMORY: 3.2 GB
^^^^^^^^
PID: 25097
COMMAND: "crash"
TASK: c000000000fedbe0 [THREAD_INFO: c00000000b190000]
CPU: 0
STATE: TASK_RUNNING (ACTIVE)
crash>
==================================
As I looked into the code I found:
The differences are observed because of the different way in which
they(proc and crash) are implemented to calculate Total Memory.
In /proc/meminfo it traverse through the memory counting each page and it has
different routines to calculate No of pages in highmem, init section, bootmem etc.
Which may be difficult to implement with Crash.
Instead we can look into sys file
implementation(/sys/devices/system/node/node<n>/meminfo). Here the Total Page is
got not from unsigned long node_spanned_pages but from long node_present_pages.
The definitions of node_present_pages says 'total number of physical pages'
while node_spanned_pages says 'total size of physical page range, including
holes'.
This is observed because of way Node 2 is spread in the machine its
pfn(physical frame number) starts from 0 while that of 0th and 1st node
starts from 4096 and 8192 pfns respectively. so node3->spanned_pages has
double counted value from even the node 0 and node 1. Hence I feel its
better to use present_pages which has only the pages from the node
excluding the holes.
======================================
The patch to fix the problem:
Let me know of your opinion..
------------------------------------------------------------------------------------------------------------------------
Name: node_present_page.patch
node_present_page.patch Type: text/x-patch
Encoding: 7bit
Hi Sharyathi,
I agree that the "MEMORY:" size output is incorrect on your
system for the reasons you have outlined.
But your proposed patch would cause other things to break,
because it would set each internal per-node "nt->size" field
to the present pages instead of the spanned pages.
Therefore, any function that uses the per-node nt->size
value -- such as dump_mem_map(), is_page_ptr(),
phys_to_page(), next_kpage(), etc...) would end up
using an incorrect, shortchanged, value.
However, the total_node_memory() function specifically
should probably use the pglist_data node_present_pages
value instead of the "nt->size" value that is based upon the
node's spanned pages.
I originally thought this might come up, as evidenced by
the fact that I initialize the "pglist_data_node_present_pages"
member offset, but don't use it anywere.
Let me tinker with this for a while...
Thanks,
Dave