Re: Locating managed objects within ObjectAlloc (was Re: Garbage collection, core data, and tight loops)

FROM : Aaron Burghardt
DATE : Mon Nov 05 04:01:01 2007

On Nov 4, 2007, at 5:36 PM, Ben Trumbull wrote:
>
> On Nov 4, 2007, at 3:27 AM, ajb.<email_removed> wrote:

>>


> No.  The relationship is more complicated.  For large blocks of 
> memory, malloc will return the allocation back to the kernel.  For 
> small blocks, it will not, but instead coalesce the free space for 
> reuse later.  The objects used in Core Data are almost exclusively 
> small.  Amit



>>      ptr = malloc(10 * 1024 * 1024);

>
> Try again with something closer to the size of your managed 
> objects.  Like 96-256 bytes.
>
> Generally, I find RSIZE to reflect the high watermark of the 
> process, and use 'heap' to examine the currently free space within 
> it.  Your mileage may vary.  There's some pretty vociferous 
> disagreement over the "ideal" way to measure memory utilization 
> (available v.s. vm deallocated v.s. internal fragmentation, etc)
>

  Yup, even 10 KB mallocs were small enough.  For anyone that may be 
following this thread, the following test looks different in Activity 
Monitor (and and presumably ObjectAlloc).  Once the VSIZE and RSIZE go 
up, they stay at that level until the test quits:

#include <stdlib.h>

int main( int argc, char *argv[])
{
    sleep(5);
    char *ptr[1000];
    int i;
    while (1) {
        for( i = 0; i < 1000; i++)
            ptr[i] = malloc(10 * 1024);
        sleep(10);

        int j;
        for( i = 0; i < 1000; i++) {
            for( j = 0; j < (10 * 1024); j++)
                *(ptr[i] + j) = 'x';
        }
        sleep(10);

        for( i = 0; i < 1000; i++)
            free(ptr[i]);
        sleep(10);
    }
}

Thanks again,

Aaron