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

Thu Mar 17 09:16:00 GMT 2005

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 2005年2月16日, 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円7円/234円0円0円0円4円17円374円0ドル20円7円/240円$0円0円B17円3円
>>>>>> 72j(177円"..., 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) ---
>>>>>> #
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>