Date: Mon, 29 Dec 2008 19:47:53 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Dan Nelson <dnelson@allantgroup.com> Cc: Yuri <yuri@rawbw.com>, freebsd-hackers@freebsd.org Subject: Re: How process size is calculated? Is it always based on the current highest available address in memory space? Message-ID: <alpine.BSF.1.10.0812291947100.9438@fledge.watson.org> In-Reply-To: <20081229154544.GB21654@dan.emsphone.com> References: <49585C75.80203@rawbw.com> <20081229154544.GB21654@dan.emsphone.com>
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On Mon, 29 Dec 2008, Dan Nelson wrote:
> 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:
You can use procstat(8), or on older versions of FreeBSD procfs, to explore
the layout of process memory, which may also lend some insight to what's going
on.
Robert N M Watson
Computer Laboratory
University of Cambridge
>
> $ ./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
> dnelson@allantgroup.com
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