[OT] Re: Controlling the garbage collector (GC) at RT?

[Martin Egholm Nielsen]

Hi Hans,

>>> You also need to touch the resulting memory.  Try something like
>>> char *v = sbrk( 1000000 );
>>> for (char *p = v; p < p + 1000000; ++p) *p = 42;
>>> in the loop.
>> I'll try something similar tomorrow, thanks alot - although I will 
>> need modify the ever true statement "p < p + 1M" to "p < v + 1M"...
> So, now I tried this:
> 
> #include <unistd.h>
> 
> int main( int i )
> {
>   while ( 1 ) {
>     char *v = sbrk( 1000000 );
>     char *p;
>     for (*p = v; p < v + 1000000; ++p) {
>       *p = 42;
>     } // for
> 
>     printf( "%x\n\n", v );
>   } // while
> } // main
> 
> And still nothing happens with the memory consumption, although the 
> pointer ends up at 0xffffffff...
Nooow, after modifying the program to

for ( p = v; ...

it "works" - the application is terminated by the kernel.
This goes regardless what [0,1,2] is echo'ed into 
"/proc/sys/vm/overcommit_memory"...
The kernel reports:

Out of Memory: Killed process 36 (sbrktest)

But what should the outcome really had been?

I tried the same on an elder kernel on a different target - 2.4.17 and 
i386 - and the same outcome...

BR,
  Martin Egholm

>>>> -----Original Message-----
>>>> From: java-owner@gcc.gnu.org [mailto:java-owner@gcc.gnu.org] On 
>>>> Behalf Of Martin Egholm Nielsen
>>>> Sent: Wednesday, February 23, 2005 12:04 AM
>>>> To: java@gcc.gnu.org
>>>> Subject: Re: Controlling the garbage collector (GC) at RT?
>>>>
>>>>
>>>>
>>>>> It seems to me that the only problem here is that this 
>>>> still seems to
>>>>> happen with overcommit-accounting set to 2.
>>>>> I would expect that you can reproduce this problem with a 
>>>> program that
>>>>> alternately allocates a few MB with sbrk, and then touches the 
>>>>> allocated memory.  If you can't, there's something really 
>>>> weird going
>>>>> on here.  If you can, it'll give you a test case for the kernel 
>>>>> people.
>>>> I tried the following:
>>>>
>>>> #include <unistd.h>
>>>>
>>>> int main( int i )
>>>> {
>>>>   while ( 1 ) {
>>>>     void *v = sbrk( 100000 );
>>>>     // sleep( 1 );
>>>>   } // while
>>>> } // main
>>>>
>>>> But that doesn't result in anything - the memory usage for the 
>>>> application does not grow...
>>>> Are there anything else I should do to allocate the memory?
>>>>
>>>> BR,
>>>>  Martin
>>>>
>>>>
>>>>> Hans
>>>>>
>>>>> On Wed, 16 Feb 2005, Martin Egholm Nielsen wrote:
>>>>>
>>>>>
>>>>>
>>>>>> Hi Hans,
>>>>>>
>>>>>>
>>>>>>
>>>>>>>>> It would indeed be interesting to know why the Linux kernel
>>>>>>
>>>>>>
>>>>>>
>>>>>>>>> kills the application rather than returning failure.
>>>>>>
>>>>>>
>>>>>>
>>>>>>>> Sure, but how to do that? Any guidelines?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> What do you see on the console?  Anything in the system log?  
>>>>>>> Does strace tell you anything?
>>>>>>
>>>>>>
>>>>>>
>>>>>> Below is the last part of "strace -f -F -i -v". It doesn't 
>>>>
>>>>
>>>>
>>>> really look
>>>>
>>>>>> like there's anything of value?
>>>>>>
>>>>>> // Martin
>>>>>>
>>>>>> [pid    75] [0f833558] write(1, "*** MEM CHUNK TAKEN: 
>>>>
>>>>
>>>>
>>>> 8388608\n", 29***
>>>>
>>>>>> MEM CHUNK TAKEN: 8388608
>>>>>> ) = 29
>>>>>> [pid    75] [0f839834] brk(0x12d15000)  = 0x12d15000
>>>>>> [pid    75] [0f839834] brk(0x12d25000)  = 0x12d25000
>>>>>> [pid    75] [0f81126c] getpid()         = 75
>>>>>> [pid    75] [0f799444] kill(77, SIGPWR <unfinished ...>
>>>>>> [pid    76] [0f840e2c] <... poll resumed> [{fd=3, events=POLLIN,
>>>>>> revents=POLLIN}
>>>>>> ], 1, 2000) = 1
>>>>>> [pid    75] [0f799444] <... kill resumed> ) = 0
>>>>>> [pid    76] [0f81127c] getppid()        = 75
>>>>>> [pid    76] [0f833548] read(3,
>>>>>> "\20\7/\234\0\0\0\4\17\374$0\20\7/\240$\0\0B\17\3
>>>>>> 72j(\177"..., 148) = 148
>>>>>> [pid    76] [0f840e2c] poll( <unfinished ...>
>>>>>> [pid    75] [0f799444] kill(77, SIGXCPU) = 0
>>>>>> [pid    75] [0f839834] brk(0x13525000)  = 0x13525000
>>>>>> [pid    75] [0f833558] write(1, "*** MEM CHUNK TAKEN: 
>>>>
>>>>
>>>>
>>>> 8388608\n", 29***
>>>>
>>>>>> MEM CHUNK TAKEN: 8388608
>>>>>> ) = 29
>>>>>> [pid    75] [0f839834] brk(0x13535000)  = 0x13535000
>>>>>> [pid    75] [0f839834] brk(0x13545000)  = 0x13545000
>>>>>> [pid    75] [0f839834] brk(0x13d45000)  = 0x13d45000
>>>>>> [pid    75] [0f833558] write(1, "*** MEM CHUNK TAKEN: 
>>>>
>>>>
>>>>
>>>> 8388608\n", 29***
>>>>
>>>>>> MEM CHUNK TAKEN: 8388608
>>>>>> ) = 29
>>>>>> [pid    76] [0f840e2c] <... poll resumed> [{fd=3, 
>>>>
>>>>
>>>>
>>>> events=POLLIN}], 1,
>>>>
>>>>>> 2000) = 0
>>>>>> [pid    76] [0f840e2c] --- SIGTERM (Terminated) ---
>>>>>> #
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
>>
> 
>