Date: Sat, 11 Jan 2003 03:35:51 -0800 From: David Schultz <dschultz@uclink.Berkeley.EDU> To: phk@FreeBSD.ORG Cc: Archie Cobbs <archie@dellroad.org>, freebsd-arch@FreeBSD.ORG Subject: Re: Virtual memory question Message-ID: <20030111113551.GC3961@HAL9000.homeunix.com> In-Reply-To: <3788.1042270528@critter.freebsd.dk> References: <200301110200.h0B20rUC024725@arch20m.dellroad.org> <3788.1042270528@critter.freebsd.dk>
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Thus spake phk@FreeBSD.ORG <phk@FreeBSD.ORG>:
> In message <200301110200.h0B20rUC024725@arch20m.dellroad.org>, Archie Cobbs wri
> tes:
>
> >The question is: how does the performance of various FreeBSD system
> >calls (especially mmap() and munmap()) degrade when a process has
> >lots and lots of tiny regions mapped into memory?
>
> Badly. At least it used to do: When I wrote phkmalloc(3) I tried
> using malloc instead of sbrk(2) and it suffered because the VM system
^^^^^^ you mean mmap(2)?
> couldn't collapse all the individual allocations (ie: N lines in
> /proc/$pid/map
The following program does 1000 mmaps of various sizes, then
prints its own memory map. It shows that the resulting vm_map has
only a few entries in both -CURRENT and -STABLE. The log for
src/sys/vm/vm_map.c suggests that the collapse code may have been
broken/non-optimal at several times during the past six years.
#include <sys/types.h>
#include <sys/mman.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#define NUM_MMAPS 1000
int main() {
int i, psize, fd, len;
char *p;
char buf[20];
psize = getpagesize();
for (i = 0; i < NUM_MMAPS; i++) {
p = mmap(NULL, psize * (i % 4 + 1), PROT_READ|PROT_WRITE,
MAP_ANON|MAP_SHARED, -1, 0);
if (p == NULL)
err(1, "mmap");
}
snprintf(buf, 20, "/proc/%u/map", getpid());
if ((fd = open(buf, O_RDONLY)) < 0)
err(1, "open");
if ((len = read(fd, p, psize - 1)) < 0)
err(1, "read");
p[len] = '\0';
printf("%s\n", p);
return 0;
}
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