Swap strangeness: total VIRT ~23mb for all processes, swap 91156k used - impossible?

From: Denis Vlasenko
Date: Thu Oct 28 2004 - 05:42:08 EST

I am playing with 'small/beautiful stuff' like
bbox/uclibc.

I ran oom_trigger soon after boot and took
"top b n 1" snapshot after OOM kill.

Output puzzles me: total virtual space taken by *all*
processes is ~23mb yet swap usage is ~90mb.

How that can be? *What* is there? Surely it can't
be a filesystem cache because OOM condition reduces that
to nearly zero.

top output
(note: some of them are busybox'ed, others are compiled
against uclibc, some are statically built with dietlibc,
rest is plain old shared binaries built against glibc):

top - 13:19:32 up 48 min, 1 user, load average: 0.25, 0.22, 0.09
Tasks: 80 total, 1 running, 79 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.2% us, 0.3% sy, 0.0% ni, 98.7% id, 0.8% wa, 0.0% hi, 0.0% si
Mem: 112376k total, 109620k used, 2756k free, 6460k buffers
Swap: 262136k total, 91156k used, 170980k free, 4700k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1204 root 15 0 1652 788 1520 R 2.0 0.7 0:00.01 top
1 root 16 0 968 12 892 S 0.0 0.0 0:01.27 init
2 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
3 root 5 -10 0 0 0 S 0.0 0.0 0:00.03 events/0
4 root 8 -10 0 0 0 S 0.0 0.0 0:00.00 khelper
23 root 5 -10 0 0 0 S 0.0 0.0 0:00.01 kblockd/0
47 root 15 0 0 0 0 S 0.0 0.0 0:00.00 pdflush
48 root 15 0 0 0 0 S 0.0 0.0 0:00.03 pdflush
50 root 14 -10 0 0 0 S 0.0 0.0 0:00.00 aio/0
49 root 15 0 0 0 0 S 0.0 0.0 0:02.15 kswapd0
51 root 15 0 0 0 0 S 0.0 0.0 0:00.00 cifsoplockd
125 root 25 0 0 0 0 S 0.0 0.0 0:00.00 kseriod
251 root 5 -10 0 0 0 S 0.0 0.0 0:00.00 reiserfs/0
273 root 18 0 1212 4 1180 S 0.0 0.0 0:00.00 udevd
479 rpc 16 0 1360 4 1308 S 0.0 0.0 0:00.00 rpc.portmap
543 root 16 0 52 16 16 S 0.0 0.0 0:00.01 svscan
556 root 17 0 348 4 316 S 0.0 0.0 0:00.00 sleep
557 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
558 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
559 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
560 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
561 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
563 root 16 0 1260 128 1228 S 0.0 0.1 0:00.02 gpm
564 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
565 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
566 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
567 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
568 user0 17 0 1660 772 1520 S 0.0 0.7 0:06.87 top
569 daemon 18 0 28 4 20 S 0.0 0.0 0:00.00 multilog
579 root 16 0 3076 3076 2456 S 0.0 2.7 0:00.02 ntpd
580 daemon 17 0 28 24 20 S 0.0 0.0 0:00.00 multilog
586 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
588 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
589 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
590 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
594 daemon 18 0 28 4 20 S 0.0 0.0 0:00.00 multilog
599 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
600 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
605 root 18 0 2492 700 2400 S 0.0 0.6 0:00.10 sshd
617 logger 17 0 28 28 20 S 0.0 0.0 0:00.00 multilog
624 root 17 0 36 28 16 S 0.0 0.0 0:00.01 socklog
632 daemon 17 0 28 4 20 S 0.0 0.0 0:00.00 multilog
636 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
637 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
643 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
644 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
647 root 16 0 44 4 36 S 0.0 0.0 0:00.00 tcpserver
648 apache 15 0 28 4 20 S 0.0 0.0 0:00.00 multilog
658 daemon 18 0 28 4 20 S 0.0 0.0 0:00.00 multilog
665 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
666 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
667 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
668 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
669 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
670 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
671 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
672 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
673 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
674 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
675 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
676 logger 16 0 36 4 16 S 0.0 0.0 0:00.00 socklog
677 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
678 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
679 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
680 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
681 root 16 0 20 4 16 S 0.0 0.0 0:00.00 supervise
685 root 16 0 1400 512 1320 S 0.0 0.5 0:00.02 automount
698 daemon 19 0 28 4 20 S 0.0 0.0 0:00.00 multilog
699 root 16 0 708 4 576 S 0.0 0.0 0:00.00 getty
704 root 17 0 1824 508 1528 S 0.0 0.5 0:00.01 login
715 logger 15 0 28 4 20 S 0.0 0.0 0:00.01 multilog
716 root 16 0 708 4 576 S 0.0 0.0 0:00.00 getty
721 root 16 0 708 4 576 S 0.0 0.0 0:00.00 getty
725 logger 16 0 28 4 20 S 0.0 0.0 0:00.00 multilog
729 root 16 0 708 4 576 S 0.0 0.0 0:00.00 getty
730 root 16 0 708 4 576 S 0.0 0.0 0:00.00 getty
731 root 16 0 708 4 576 S 0.0 0.0 0:00.00 getty
1097 root 15 0 1216 576 892 S 0.0 0.5 0:00.01 bash
1196 root 15 0 0 0 0 S 0.0 0.0 0:00.00 rpciod
1197 root 19 0 0 0 0 S 0.0 0.0 0:00.00 lockd

oom_trigger.c:

#include <stdlib.h>
int main() {
void *p;
unsigned size = 1<<20;
unsigned long total=0;
while(size) {
p = malloc(size);
if(!p) size>>=1;
else {
memset(p, 0x77, size);
total+=size;
printf("Allocated %9u bytes, %12lu total\n",size,total);
}
}
return 0;
}

--
vda

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