Date: Sun, 11 Apr 1999 21:11:08 -0400 (EDT) From: Brian Feldman <green@unixhelp.org> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: current@FreeBSD.ORG Subject: Re: swap-related problems Message-ID: <Pine.BSF.4.05.9904112100260.35407-100000@janus.syracuse.net> In-Reply-To: <199904120004.RAA08629@apollo.backplane.com>
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On Sun, 11 Apr 1999, Matthew Dillon wrote:
> :It seems that something has broken the good ol' swap behavior. For instance,
> :I have my user-limits set to unlimited and I run something which uses up
> :all RAM. Mallocing never FAILS in the program, as brk() doesn't fail, as etc
> :etc etc. But mallocing continues, all swap space gets used, and both the
> :runaway process and the next biggest gets killed (XF86, of course).
> : Matt, perhaps you can shed light on
> : a. why mallocs still succeed after
> :swap_pager: out of swap space
> :swap_pager_getswapspace: failed
> : is displayed
> : b. why the process continues and gets killed TWICE, or two different
> : processes get killed
> :?
> :
> : Brian Feldman _ __ ___ ____ ___ ___ ___
>
> The thing with the processes getting killed twice or two different
> processes being killed is due to the latency between sending the signal
> to kill the process and the process actually going away. In order to be
> killed, the process must be woken up and allowed to run.
Then let's make sure the kill waits before it does that.
>
> malloc() still succeeds because it isn't actually touching the new memory,
> and so the system doesn't actually reserve the memory as of the time of
> the system call. That is done by the user program later on after malloc()
> returns. malloc()'s limitations are based on the process resources, not
> available memory.
I use the memory as soon as it's malloced. If it reserves a page, then
pagefaults it into existence, the VM system knows that that page is now
allocated. When I malloc the last available page for user use, the VM
system knows that it's the last page. I dirty it, and there are none
free. If I malloc(), I want to know that there is no more memory, not
have my process killed. This is POMA.
Previously, the POLA, a NULL getting returned, WORKED CORRECTLY. It did this
for a long time. My little test program always showed this, and shows
that now something was broken. I'll attach it to the end.
>
> It would not be appropriate to make malloc() fail in this situation because
> this would result in N random programs getting malloc() failures rather
> then one or two processes getting killed. Having N random processes get
> malloc() failures can lead to serious instability with processes.
Only bad code doesn't check return values of malloc().
>
> What might help in a situation like this would a way to flag certain
> processes as being 'very important' ... that should only be killed as
> a last resort, even if they have a relatively large RSS.
Yes, I was thinking of something like this for the X server.
>
> -Matt
> Matthew Dillon
> <dillon@backplane.com>
>
>
Brian Feldman _ __ ___ ____ ___ ___ ___
green@unixhelp.org _ __ ___ | _ ) __| \
FreeBSD: The Power to Serve! _ __ | _ \__ \ |) |
http://www.freebsd.org _ |___/___/___/
ts=4
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 1024*1024
#ifdef OTHER_VER
const unsigned int junk[] = {
0xdeadbeef,
0xbeeff00d,
0x133751ff,
0xf33db34f
};
#endif
void
main(void) {
int count, yep = 0;
void *stfu[SIZE];
void *mem;
for (count = 0; count < SIZE; count++) {
if ((mem = stfu[count] = malloc(1024))) {
int where;
printf("%p (%i) malloc'd\n", stfu[count], count);
for (where = 0; where < (1024 / sizeof(unsigned)); where++)
((unsigned *)mem)[where] =
#ifdef OTHER_VER
junk[
#endif
where
#ifdef OTHER_VER
% 4]
#endif
;
yep++;
}
else
break;
}
/* free(stfu[yep--]); */
for (count = 0; count < yep; count++) {
int where;
mem = stfu[count];
for (where = 0; where < (1024 / sizeof(unsigned)); where++)
if (((unsigned *)mem)[where] !=
#ifdef OTHER_VER
junk[
#endif
where
#ifdef OTHER_VER
% 4]
#endif
) {
fprintf(stderr, "memory check failed at %i of %i:\n"
"%#x != %#x\n", count, yep,
((unsigned *)mem)[where],
#ifdef OTHER_VER
junk[
#endif
where
#ifdef OTHER_VER
% 4]
#endif
);
exit(2);
}
free(stfu[count]);
printf("%i free'd\n", count);
}
if (yep != SIZE) {
printf("mallocs failed at %i\n", yep);
exit (1);
}
else
exit (0);
}
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