powerpc64 malloc limit?

[Andreas Tobler]

On 30.11.11 22:24, Kostik Belousov wrote:
> On Wed, Nov 30, 2011 at 09:58:19PM +0100, Andreas Tobler wrote:
>> On 30.11.11 21:01, Kostik Belousov wrote:
>>> On Wed, Nov 30, 2011 at 06:44:21PM +0100, Andreas Tobler wrote:
>>>> On 30.11.11 18:09, Kostik Belousov wrote:
>>>>> On Wed, Nov 30, 2011 at 05:53:04PM +0100, Andreas Tobler wrote:
>>>>>> On 30.11.11 17:22, Kostik Belousov wrote:
>>>>>>> On Wed, Nov 30, 2011 at 06:24:41AM +0100, Andreas Tobler wrote:
>>>>>>>> All,
>>>>>>>>
>>>>>>>> while working on gcc I found a very strange situation which renders my
>>>>>>>> powerpc64 machine unusable.
>>>>>>>> The test case below tries to allocate that much memory as 'wanted'.
>>>>>>>> The
>>>>>>>> same test case on amd64 returns w/o trying to allocate mem because the
>>>>>>>> size is far to big.
>>>>>>>>
>>>>>>>> I couldn't find the reason so far, that's why I'm here.
>>>>>>>>
>>>>>>>> As Nathan pointed out the VM_MAXUSER_SIZE is the biggest on powerpc64:
>>>>>>>> #define VM_MAXUSER_ADDRESS      (0x7ffffffffffff000UL)
>>>>>>>>
>>>>>>>> So, I'd expect a system to return an allocation error when a user
>>>>>>>> tries
>>>>>>>> to allocate too much memory and not really trying it and going to be
>>>>>>>> unusable. Iow, I'd exepect the situation on powerpc64 as I see on
>>>>>>>> amd64.
>>>>>>>>
>>>>>>>> Can anybody explain me the situation, why do I not have a working
>>>>>>>> limit
>>>>>>>> on powerpc64?
>>>>>>>>
>>>>>>>> The machine itself has 7GB RAM and 12GB swap. The amd64 where I
>>>>>>>> compared
>>>>>>>> has around 4GB/4GB RAM/swap.
>>>>>>>>
>>>>>>>> TIA,
>>>>>>>> Andreas
>>>>>>>>
>>>>>>>> include<stdlib.h>
>>>>>>>> #include<stdio.h>
>>>>>>>>
>>>>>>>> int main()
>>>>>>>> {
>>>>>>>>           void *p;
>>>>>>>>
>>>>>>>>           p = (void*) malloc (1152921504606846968ULL);
>>>>>>>>           if (p != NULL)
>>>>>>>>                   printf("p = %p\n", p);
>>>>>>>>
>>>>>>>>           printf("p = %p\n", p);
>>>>>>>>           return (0);
>>>>>>>> }
>>>>>>>
>>>>>>> First, you should provide details of what consistutes 'the unusable
>>>>>>> machine situation' on powerpc.
>>>>>>
>>>>>> I can not login anymore, everything is stuck except the core control
>>>>>> mechanisms for example the fan controller.
>>>>>>
>>>>>> Top reports 'ugly' figures, below from a earlier try:
>>>>>>
>>>>>> last pid:  6790;  load averages:  0.78,  0.84,  0.86    up 0+00:34:52
>>>>>> 22:42:29 47 processes:  1 running, 46 sleeping
>>>>>> CPU:  0.0% user,  0.0% nice, 15.4% system, 11.8% interrupt, 72.8% idle
>>>>>> Mem: 5912M Active, 570M Inact, 280M Wired, 26M Cache, 104M Buf, 352K
>>>>>> Free
>>>>>> Swap: 12G Total, 9904M Used, 2383M Free, 80% Inuse, 178M Out
>>>>>>
>>>>>>     PID USERNAME    THR PRI NICE   SIZE    RES STATE   C   TIME   WCPU
>>>>>> COMMAND
>>>>>>    6768 andreast      1  52    01073741824G  6479M pfault  1   0:58
>>>>>> 18.90% 31370.
>>>>>>
>>>>>> And after my mem and swap are full I see swap_pager_getswapspace(16)
>>>>>> failed.
>>>>>>
>>>>>> In this state I can only power-cycle the machine.
>>>>>>
>>>>>>> That said, on amd64 the user map is between 0 and 0x7fffffffffff, which
>>>>>>> obviously less then the requested allocation size 0x100000000000000.
>>>>>>> If you look at the kdump output on amd64, you will see that malloc()
>>>>>>> tries to mmap() the area, fails and retries with obreak(). Default
>>>>>>> virtual memory limit is unlimited, so my best quess is that on amd64
>>>>>>> vm_map_findspace() returns immediately.
>>>>>>>
>>>>>>> On powerpc64, I see no reason why vm_map_entry cannot be allocated, but
>>>>>>> please note that vm object and pages shall be only allocated on demand.
>>>>>>> So I am curious how does your machine breaks and where.
>>>>>>
>>>>>> I would expect that the 'system' does not allow me to allocate that much
>>>>>> of ram.
>>>>>
>>>>> Does the issue with machine going into limbo reproducable with the code
>>>>> you posted ?
>>>>
>>>> If I understand you correctly, yes. I can launch the test case and the
>>>> machine is immediately unusable. Means I can not kill the process nor
>>>> can I log in. Also, top does not show anything useful.
>>> Again, let me restate my question: the single mmap() of the huge size is
>>> enough for powerpc64 machine to break apart ?
>>
>> I can't answer. I don't know yet.
>>
>>> What happen if you insert sleep(1000000); call before return ? Do not kill
>>> the process, I want to know is machine dead while the process sleeps.
>>
>> Ok, during the 'sleep' the machine is usable. top is reporting figures,
>> I can log in and edit files. The process runs now for aboutt 30'.
>>
>> When I kill the process, I do not get back to the shell nor can I log
>> in. Also top stops reporting.
>> But as you said, I didn't kill in this run.
> Then, as Alan Cox pointed out, caused by the approach taken in powerpc64
> pmap to handle pmap_remove(). It is definitely arch-specific.

Ok. I think you mean moea64_remove which is pmap_remove, right?

Where did Alan pointed this out?

Thank you for the analysis.

Andreas