[Bug 523024] [NEW] system thrashes even with lots of free memory

[Russell Robinson]

Public bug reported:

Hi,

I run two VMware guests on a Karmic 64 bit host with 4GB of RAM, and
16GB of swap.  The host is a Dell notebook and the first 8GB of swap is
on another drive (other than the internal disk).

One guest is WinXP with 512MB allocated to it.

The other is a Linux guest with 1200MB allocated to it.

The host system can thrash for an hour or more, unexpectedly, even
though it has 600MB of free RAM.

During the thrash, another 300MB might be freed - the system now has
nearly 25% memory free and it's still thrashing!  Generally, I have to
login via a remote SSH session and try to suspend one of the guests to
get the thrashing to stop - or just wait.

This happened with overcommit_memory=2 and overcommit_ratio=10,
swappiness=60

I've since changed to overcommit_memory=0 and reduced the Linux guest to
640MB.

The host now runs with around 200-300MB of free RAM, but can still
unexpectedly start thrashing again.  Though, it *only* thrashes for 15 -
20 minutes in this condition, freeing up another 100MB or so.

In both cases the WinXP guest is idle and the Linux guest is idle except
for every 15 minutes it does an "rsync" of a home directory (mostly
unchanged mailboxes) to the host via TCP.

How can a kernel thrash when it has around 20% of it's RAM free?

I've been working on this problem for 3 months.  I initially blamed
VMware, but it also happens with VirtualBox.  I've also tried various
settings including swappiness=0.

When it looked like it was the main disk was just taking too long to get
thru all the I/O, I put the first 8GB of swap on an external drive (an
SSD with confirmed read performance of 120MB/s and write performance of
30MB/s).

This now shows the main hard disk as being relatively idle during the
thrashing.

Which I think confirms the problem is not I/O bounding but a broken VM
system that's chasing its tail.

If this is not accepted as a bug, please briefly explain the logic that
says the kernel VM can thrash with 20-25% free RAM, or point me to
documents that explain it.

thanks & regards,
RR

ProblemType: Bug
Architecture: amd64
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: STAC92xx Analog [STAC92xx Analog]
   Subdevices: 2/2
   Subdevice #0: subdevice #0
   Subdevice #1: subdevice #1
AudioDevicesInUse:
 USER        PID ACCESS COMMAND
 /dev/snd/controlC0:  russellr   5714 F.... pulseaudio
CRDA: Error: [Errno 2] No such file or directory
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xf6adc000 irq 21'
   Mixer name	: 'Intel G45 DEVCTG'
   Components	: 'HDA:111d76b2,1028024f,00100302 HDA:14f12c06,14f1000f,00100000 HDA:80862802,80860101,00100000'
   Controls      : 32
   Simple ctrls  : 19
Date: Wed Feb 17 16:33:02 2010
DistroRelease: Ubuntu 9.10
HibernationDevice: RESUME=UUID=9d72666c-1de4-483e-aad6-71ec43ff0efd
MachineType: Dell Inc. Latitude E6500
Package: linux-generic 2.6.31.19.32
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcCmdLine: root=UUID=79ea59e1-891a-4774-a9be-25cb1668489c ro quiet splash
ProcEnviron:
 PATH=(custom, user)
 LANG=en_AU.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-19.56-generic
RelatedPackageVersions:
 linux-backports-modules-2.6.31-19-generic N/A
 linux-firmware 1.25
SourcePackage: linux-meta
Uname: Linux 2.6.31-19-generic x86_64
UserAsoundrc:
 pcm.btheadset {
         type bluetooth
         device 00:03:89:AB:E1:17
         profile "auto"
 }
WpaSupplicantLog:
 
dmi.bios.date: 07/31/2009
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A14
dmi.board.name: 0W612R
dmi.board.vendor: Dell Inc.
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA14:bd07/31/2009:svnDellInc.:pnLatitudeE6500:pvr:rvnDellInc.:rn0W612R:rvr:cvnDellInc.:ct8:cvr:
dmi.product.name: Latitude E6500
dmi.sys.vendor: Dell Inc.

** Affects: linux-meta (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug

-- 
system thrashes even with lots of free memory
https://bugs.launchpad.net/bugs/523024
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