Hello,
I am observing some strangeness with KVM memory usage lately. Unfortunately
hard to tell since which kernel, but if I have to guess, with 4.14 in general,
as opposed to 4.9 previously.
First, the memory usage of VMs is reported bizarrely in top:
------
KiB Mem: 16326888 total, 16016944 used, 309944 free, 118712 buffers
KiB Swap: 8388604 total, 4864 used, 8383740 free. 8797796 cached Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
12813 root 20 0 3038684 0.012t 4496 S 4.6 81.9 543:07.22 kvm-a
24701 root 20 0 1800876 0.011t 4316 R 16.9 74.4 774:30.35 kvm-b
6547 root 20 0 1639372 3.494g 5124 S 2.0 22.4 274:32.05 kvm-c
16775 root 10 -10 1468384 2.715g 4376 S 1.0 17.4 757:57.86 kvm-d
23821 root 20 0 2972160 2.036g 4284 S 18.9 13.1 3964:45 kvm-e
1016 www-data 20 0 183528 43196 8244 S 0.0 0.3 0:06.53 smokeping.+
941 smokepi+ 20 0 174020 31560 3664 S 0.0 0.2 0:18.19 /usr/sbin/+
----
As you can see the top two use 12GB and 11GB respectively as "Resident".
These grew steadily to this point over some time since VMs were launched.
But that usage is actually nowhere near the case, as the host machine only
has 7GB of RAM used in total:
# free -m
total used free shared buffers cached
Mem: 15944 15641 303 10 115 8591
-/+ buffers/cache: 6933 9010
Swap: 8191 4 8187
And the first VM listed only has 2GB of RAM allocated to it:
root 12813 1 3 Jan26 ? 09:03:09 qemu-system-x86_64 -enable-kvm
-daemonize -monitor unix:./monitor,server,nowait -name a,process=kvm-a
-smp 4 -m 2048 -device virtio-scsi-pci,id=scsi -device scsi-hd,drive=hd -drive
if=none,id=hd,cache=none,aio=native,format=raw,file=/dev/vg/vm-a,discard=unmap,detect-zeroes=off
-device virtio-net-pci,netdev=net0,mac=xx:xx:xx:xx:xx:xx -netdev
tap,vhost=on,id=net0,script=/path/to/xyz.sh -vnc [::]:1 -cpu
host,host-cache-info=on -balloon virtio -machine q35,accel=kvm
Next ones are about the same, 1 or 2 GB RAM each. One is 512MB (the one showing 2.7 GB used now...)
Secondly, I use (or try to use) KSM. At some point its efficiency dropped
like a rock. If before I had numbers like 2GB stored in 100 MB, now I only have:
/sys/kernel/mm/ksm/full_scans:1482
/sys/kernel/mm/ksm/max_page_sharing:256
/sys/kernel/mm/ksm/merge_across_nodes:1
/sys/kernel/mm/ksm/pages_shared:98528
/sys/kernel/mm/ksm/pages_sharing:104775
/sys/kernel/mm/ksm/pages_to_scan:128
/sys/kernel/mm/ksm/pages_unshared:1138639
/sys/kernel/mm/ksm/pages_volatile:184595
/sys/kernel/mm/ksm/run:1
/sys/kernel/mm/ksm/sleep_millisecs:100
/sys/kernel/mm/ksm/stable_node_chains:9
/sys/kernel/mm/ksm/stable_node_chains_prune_millisecs:2000
/sys/kernel/mm/ksm/stable_node_dups:47
/sys/kernel/mm/ksm/use_zero_pages:1
Running: 1
Sharing: 409.28 MB stored in 384.88 MB (1.06:1)
Which is somewhat strange considering 3 of the running VMs are Windows, and 2 are Debian,
shouldn't they have more "in common".
Tried with "use_zero_pages" set to 0 and 1, "1" sounded like a better idea, but it doesn't
seem to change anything.
So the question is, is there something wrong going on with KVM's RAM usage
on my system, could this be a recent bug, or have I misconfigured something.
Transparent hugepages come to mind for some reason, and I do have
TRANSPARENT_HUGEPAGE_ALWAYS=y
But while that could explain low KSM results (could it?), it shouldn't cause these
memleak-looking readings in 'top', right?
--
With respect,
Roman
