steady decrease in available memory (RAM) under 16.04

[Christopher Barrington-Leigh]

I've just upgraded to 16.04 from 15.10, and now the memory usage steadily increases from when I first boot up. After just an hour or two, all 20GB of RAM is used up, even if nothing is running, and I am forced to reboot (rebooting frequently is incompatible with my normal tasks).

Here is output from free, spaced about half a second apart:

[0753][me@-t450s:~]$ free -m
              total used free shared buff/cache available
Mem: 19958 1001 5808 7147 13148 11648
Swap: 20358 0 20358
[0753][me@-t450s:~]$ free -m
              total used free shared buff/cache available
Mem: 19958 1001 5806 7148 13151 11647
Swap: 20358 0 20358
[0753][me@-t450s:~]$ free -m
              total used free shared buff/cache available
Mem: 19958 1001 5804 7149 13153 11646
Swap: 20358 0 20358
[0753][me@-t450s:~]$ free -m
              total used free shared buff/cache available
Mem: 19958 1001 5801 7151 13156 11644
Swap: 20358 0 20358

htop shows that 8GB is in use, although there are no applications using much. I understand from free that it is all buffered/cached?

Both htop and free suggest that the memory is really not available.
I do not know where it is going.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.4.0-22-generic 4.4.0-22.40
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC2: cpbl 2571 F.... pulseaudio
 /dev/snd/controlC1: cpbl 2571 F.... pulseaudio
 /dev/snd/controlC0: cpbl 2571 F.... pulseaudio
CurrentDesktop: Unity
Date: Wed May 25 07:54:14 2016
EcryptfsInUse: Yes
HibernationDevice: RESUME=UUID=e5d0a2bb-27cf-494a-849c-1985d165fbd7
InstallationDate: Installed on 2016-02-12 (102 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
MachineType: LENOVO 20BXCTO1WW
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-22-generic.efi.signed root=UUID=ea2fb511-8d62-4b96-bdaa-4b3f7bf79cc6 ro noprompt quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-22-generic N/A
 linux-backports-modules-4.4.0-22-generic N/A
 linux-firmware 1.157
SourcePackage: linux
UpgradeStatus: Upgraded to xenial on 2016-05-24 (0 days ago)
dmi.bios.date: 11/06/2015
dmi.bios.vendor: LENOVO
dmi.bios.version: JBET54WW (1.19 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20BXCTO1WW
dmi.board.vendor: LENOVO
dmi.board.version: SDK0J40697 WIN
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.modalias: dmi:bvnLENOVO:bvrJBET54WW(1.19):bd11/06/2015:svnLENOVO:pn20BXCTO1WW:pvrThinkPadT450s:rvnLENOVO:rn20BXCTO1WW:rvrSDK0J40697WIN:cvnLENOVO:ct10:cvrNone:
dmi.product.name: 20BXCTO1WW
dmi.product.version: ThinkPad T450s
dmi.sys.vendor: LENOVO

[Brad Figg (brad-figg)]

This change was made by a bot.

[penalvch (penalvch)]

Christopher Barrington-Leigh, thank you for reporting this and helping make Ubuntu better.

In order to allow additional upstream developers to examine the issue, at your earliest convenience, could you please test the latest upstream kernel available from http://kernel.ubuntu.com/~kernel-ppa/mainline/?C=N;O=D ? Please keep in mind the following:
1) The one to test is at the very top line at the top of the page (not the daily folder).
2) The release names are irrelevant.
3) The folder time stamps aren't indicative of when the kernel actually was released upstream.
4) Install instructions are available at https://wiki.ubuntu.com/Kernel/MainlineBuilds .

If testing on your main install would be inconvenient, one may:
1) Install Ubuntu to a different partition and then test this there.
2) Backup, or clone the primary install.

If the latest kernel did not allow you to test to the issue (ex. you couldn't boot into the OS) please make a comment in your report about this, and continue to test the next most recent kernel version until you can test to the issue. Once you've tested the upstream kernel, please comment on which kernel version specifically you tested. If this issue is fixed in the mainline kernel, please add the following tags by clicking on the yellow circle with a black pencil icon, next to the word Tags, located at the bottom of the report description:
kernel-fixed-upstream
kernel-fixed-upstream-X.Y-rcZ

Where X, and Y are the first two numbers of the kernel version, and Z is the release candidate number if it exists.

If the mainline kernel does not fix the issue, please add the following tags:
kernel-bug-exists-upstream
kernel-bug-exists-upstream-X.Y-rcZ

Please note, an error to install the kernel does not fit the criteria of kernel-bug-exists-upstream.

Also, you don't need to apport-collect further unless specifically requested to do so.

Once testing of the latest upstream kernel is complete, please mark this report Status Confirmed. Please let us know your results.

Thank you for your understanding.

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]