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

[Martin Egholm Nielsen <martin at egholm-nielsen dot dk>]

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) ---
> > > > > > #