[Crash-utility] Need to update page->flags

[David Wilder]

Dave Anderson wrote:

> David Wilder wrote:
>
>> The definitions for page->flags in crash are no longer correct in crash
>> resulting in incorrect output for the kmem -i command.   The page flags
>> are currently defined for V22 V24 and one flag for V26.    The flag
>> definitions are changing in the 2.6 kernel often, crash will need to
>> update these definitions for each 2.6.x.  Yuck!    Can we limit the flag
>> definitions to just a few kernel versions?  Any suggestions on what
>> versions we should have definitions for?
>>  
>
> I've long since been keeping up with these, because most
> of the hardwired page flag definitions that are #define'd
> in memory.c are not used anymore.  For example, there's
> this construct in dump_mem_map() which just displays the
> hex value:
>
>   if (v22) {
>        ...translate hardwired flags...
>   } else if (THIS_KERNEL_VERSION > LINUX(2,4,9)) {
>        fprintf(fp, "%lx\n", flags);
>   } else {
>        ...translate old hardwired 2.4 flags...
>   }
>
> But there are a few other places that need to know about
> specific flags, like PG_reserved and PG_slab for example,
> whose bits get determined in vm_init().  Which one has
> changed that upsets "kmem -i"?
>
> Dave
>

I was first looking at PG_slab.  But I now see this bit in vm_init()

if (VALID_MEMBER(page_pte)) {
                if (THIS_KERNEL_VERSION < LINUX(2,6,0))
                        vt->PG_slab = 10;
                else if (THIS_KERNEL_VERSION >= LINUX(2,6,0))
                        vt->PG_slab = 7;
        }

This would set the correct value for vt->PG_slab = 7 except that  pte is 
not a member of the struct page so vt->PG_slab=0.

vt->PG_reserved is not getting set in PG_reserved_flag_init().  But that 
looks like a problem resolving the symbol sys_read.   So in 
dump_mem_map() it is falling back to v24_PG_reserved....

case GET_TOTALRAM_PAGES:
                                if (vt->PG_reserved)
                                        PG_reserved_flag = vt->PG_reserved;
                                else
                                        PG_reserved_flag = v22 ?
                                                1 << v22_PG_reserved :
                                                1 << v24_PG_reserved;
....
That should mess up the calculation for total memory for kmem -i.  But 
in my case the number is still correct..





-- 
David Wilder
IBM Linux Technology Center
Beaverton, Oregon, USA 
dwilder at us.ibm.com
(503)578-3789