Date: Wed, 30 Nov 2011 21:58:19 +0100 From: Andreas Tobler <andreast-list@fgznet.ch> To: Kostik Belousov <kostikbel@gmail.com> Cc: FreeBSD Arch <freebsd-arch@freebsd.org> Subject: Re: powerpc64 malloc limit? Message-ID: <4ED698EB.8090904@fgznet.ch> In-Reply-To: <20111130200103.GE50300@deviant.kiev.zoral.com.ua> References: <4ED5BE19.70805@fgznet.ch> <20111130162236.GA50300@deviant.kiev.zoral.com.ua> <4ED65F70.7050700@fgznet.ch> <20111130170936.GB50300@deviant.kiev.zoral.com.ua> <4ED66B75.3060409@fgznet.ch> <20111130200103.GE50300@deviant.kiev.zoral.com.ua>
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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.
Thanks,
Andreas
[bohrium:~] andreast% ./mega_malloc
p = 0x50400000
p = 0x50400000
...
last pid: 1279; load averages: 0.05, 0.03, 0.04 up 0+00:30:34
21:56:40
41 processes: 1 running, 40 sleeping
CPU: 0.0% user, 0.0% nice, 1.2% system, 0.2% interrupt, 98.6% idle
Mem: 28M Active, 26M Inact, 89M Wired, 8K Cache, 725M Buf, 6642M Free
Swap: 12G Total, 12G Free
PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU
COMMAND
1219 andreast 1 24 01073741824G 1608K nanslp 0 0:00
0.00% mega_m
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