In the last episode (Dec 28), Yuri said:
> malloc(3) can be controlled by MALLOC_OPTIONS to use mmap-based
> allocation as opposed to sbrk-based allocation. But
> allocations/deallocations with mmaps can eventually lead to
> non-continuously mmapped memory (having some non-mmapped gaps).
>
> Are these gaps excluded from the process size or size is always
> linked to the current highest available address in memory space?
It looks like only mapped memory is counted in process size. The test
program below shows that the reported size goes down, even if a memory
range inbetween two others is unmapped:
$ ./mmap
Before mmap:
UID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND
1000 48058 62165 0 8 0 1928 824 wait S+ ph 0:00.01 ./mmap
mmap 64MB A=0x28280000
UID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND
1000 48058 62165 0 8 0 67464 824 wait S+ ph 0:00.01 ./mmap
mmap 64MB B=0x2c280000
UID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND
1000 48058 62165 0 8 0 133000 824 wait S+ ph 0:00.01 ./mmap
mmap 64MB C=0x30280000
UID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND
1000 48058 62165 0 8 0 198536 824 wait S+ ph 0:00.01 ./mmap
munmap B
UID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND
1000 48058 62165 0 8 0 133000 824 wait S+ ph 0:00.01 ./mmap
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>
int main(void)
{
char *cmd;
void *a, *b, *c;
asprintf(&cmd, "ps axlp %d", getpid());
printf("Before mmap:\n");
system(cmd);
a = mmap(NULL, 64 * 1024 * 1024, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
printf("mmap 64MB A=%p\n", a);
system(cmd);
b = mmap(NULL, 64 * 1024 * 1024, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
printf("mmap 64MB B=%p\n", b);
system(cmd);
c = mmap(NULL, 64 * 1024 * 1024, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
printf("mmap 64MB C=%p\n", c);
system(cmd);
printf("munmap B\n");
munmap(b, 64 * 1024 * 1024);
system(cmd);
return 0;
}
--
Dan Nelson
dnel...@allantgroup.com
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