Excessive swapping in spite of lots of free memory
From: Daniel Brockhaus
Date: Fri Oct 10 2003 - 18:06:34 EST
Hi there,
I hope I'm not reporting old news here. I've searched the archive and the
FAQ, but couldn't find anything. Anyway. Here's the problem:
Ever since I moved from Redhat 7.1 to Redhat 9 (don't remember the old
kernel version I'm afraid) I had trouble with the system swapping like mad.
The best example is a computer with 256MB RAM, of which 90MB are used (the
kernel uses the remaining 160MB for harddisk cache/buffers). But I still
get about 10 writes and 0.3 reads per second to the swap partition (as
reported by sar and iostat). I don't mind the reads but the writes are...
excessive.
I've solved the problem for this server by disabling swap - and it works
without any problems - but on the other computers I don't have that much
memory to spare, and I'd really like to have the swap space as a "reserve",
in case memory gets tight.
I'm running three computers, all of which show this behaviour. They are
running no processes besides the essentials (syslogd, klogd, crond, atd,
mingetty, ntpd, sshd and sendmail, plus the usual kernel processes) and a
server for an online game. This game server (and I assume it is the one
causing the "bug") uses anonymous mmap() to allocate memory. It allocates
about 25MB in 14 areas which are grown or shrunk, depending on the memory
needs in that particular area.
Is this a known problem? Are there any workarounds? Is there anything I can
do besides buy more RAM and disable swap everywhere?
I won't be able to do a lot of testing, I'm afraid, and I cannot move to
any "unstable" development kernel. It is a commercial setup, and every
downtime or crash is expensive.
Here's some more info about the computer I mentioned above. Let me know if
you need anything else:
# cat /proc/version
Linux version 2.4.20-19.9 (bhcompile@xxxxxxxxxxxxxxxxxxxxxxxxxx) (gcc
version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)) #1 Tue Jul 15 17:18:13 EDT 2003
# cat /proc/meminfo
total: used: free: shared: buffers: cached:
Mem: 261378048 256589824 4788224 0 50667520 110481408
Swap: 0 0 0
MemTotal: 255252 kB
MemFree: 4676 kB
MemShared: 0 kB
Buffers: 49480 kB
Cached: 107892 kB
SwapCached: 0 kB
Active: 184712 kB
ActiveAnon: 71452 kB
ActiveCache: 113260 kB
Inact_dirty: 1192 kB
Inact_laundry: 39564 kB
Inact_clean: 4492 kB
Inact_target: 45992 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 255252 kB
LowFree: 4676 kB
SwapTotal: 0 kB
SwapFree: 0 kB
# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 1
model name : Intel(R) Pentium(R) 4 CPU 1.70GHz
stepping : 2
cpu MHz : 1697.167
cache size : 256 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 3381.65
# cat /proc/pci
PCI devices found:
Bus 0, device 0, function 0:
Host bridge: VIA Technologies, Inc. VT8753 [P4X266 AGP] (rev 1).
Master Capable. Latency=8.
Prefetchable 32 bit memory at 0xe0000000 [0xe7ffffff].
Bus 0, device 1, function 0:
PCI bridge: VIA Technologies, Inc. VT8633 [Apollo Pro266 AGP] (rev 0).
Master Capable. No bursts. Min Gnt=12.
Bus 0, device 9, function 0:
RAID bus controller: 3ware Inc 3ware 7000-series ATA-RAID (rev 1).
IRQ 12.
Master Capable. Latency=32. Min Gnt=9.
I/O at 0xd000 [0xd00f].
Non-prefetchable 32 bit memory at 0xec821000 [0xec82100f].
Non-prefetchable 32 bit memory at 0xec000000 [0xec7fffff].
Bus 0, device 11, function 0:
Ethernet controller: Intel Corp. 82557/8/9 [Ethernet Pro 100] (rev 12).
IRQ 5.
Master Capable. Latency=32. Min Gnt=8.Max Lat=56.
Non-prefetchable 32 bit memory at 0xec820000 [0xec820fff].
I/O at 0xd400 [0xd43f].
Non-prefetchable 32 bit memory at 0xec800000 [0xec81ffff].
Bus 0, device 17, function 0:
ISA bridge: VIA Technologies, Inc. VT8233 PCI to ISA Bridge (rev 0).
Bus 0, device 17, function 1:
IDE interface: VIA Technologies, Inc. VT82C586B PIPC Bus Master IDE
(rev 6).
Master Capable. Latency=32.
I/O at 0xd800 [0xd80f].
Bus 0, device 17, function 2:
USB Controller: VIA Technologies, Inc. USB (rev 27).
IRQ 5.
Master Capable. Latency=32.
I/O at 0xdc00 [0xdc1f].
Bus 0, device 17, function 3:
USB Controller: VIA Technologies, Inc. USB (#2) (rev 27).
IRQ 5.
Master Capable. Latency=32.
I/O at 0xe000 [0xe01f].
Bus 0, device 17, function 4:
USB Controller: VIA Technologies, Inc. USB (#3) (rev 27).
IRQ 5.
Master Capable. Latency=32.
I/O at 0xe400 [0xe41f].
Bus 1, device 0, function 0:
VGA compatible controller: ATI Technologies Inc Rage XL AGP 2X (rev 101).
IRQ 11.
Master Capable. Latency=32. Min Gnt=8.
Non-prefetchable 32 bit memory at 0xe8000000 [0xe8ffffff].
I/O at 0xc000 [0xc0ff].
Non-prefetchable 32 bit memory at 0xea000000 [0xea000fff].
# cat /proc/modules
autofs 13268 0 (autoclean) (unused)
e100 54564 1
ipt_REJECT 3992 6 (autoclean)
iptable_filter 2412 1 (autoclean)
ip_tables 15096 2 [ipt_REJECT iptable_filter]
keybdev 2976 0 (unused)
mousedev 5556 0 (unused)
hid 22244 0 (unused)
input 5856 0 [keybdev mousedev hid]
usb-uhci 26412 0 (unused)
usbcore 79040 1 [hid usb-uhci]
ext3 70784 2
jbd 51924 2 [ext3]
3w-xxxx 39360 2
sd_mod 13452 4
scsi_mod 107512 2 [3w-xxxx sd_mod]
Thanks a lot for your help,
Daniel
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