Update: TMEM has been removed. The latest uptream version containing it seems to be 5.2, namely revision v5.2.21.
Tested with XEN version 4.11.0 and domU versions 4.18.16 & 5.2.14.
make defconfig make xenconfig
eventually disable DOM0 and enable
CONFIG_XEN_SELFBALLOONING=y CONFIG_XEN_TMEM=m
deliver the modules into the guest’s /lib/modules/$version/ and once booted, load
modprobe tmem echo tmem >> /etc/modules
gives
[ 37.471390] xen:tmem: frontswap enabled, RAM provided by Xen Transcendent Memory [ 37.471410] xen:tmem: cleancache enabled, RAM provided by Xen Transcendent Memory [ 37.471423] xen_selfballoon: Initializing Xen selfballooning driver [ 37.471425] xen_selfballoon: Initializing frontswap selfshrinking driver
we end-up with ilding guests eating very few memory (after a few minutes of progressive shrinking)
slack 871-873 stretch 903-906 bionic 104
values taken from free -m e.g.
total used free shared buff/cache available Mem: 104 80 5 0 18 12 Swap: 0 0 0
While stress-testing RAM with DD against TMPFS
[ 1934.161197] Out of memory: Killed process 1413 ((sd-pam)) total-vm:108836kB, anon-rss:1840kB, file-rss:0kB, shmem-rss:0kB
[ 1934.166271] Out of memory: Killed process 1430 (dd) total-vm:7352kB, anon-rss:1124kB, file-rss:0kB, shmem-rss:0kB
Killed
[ 1935.132381] Out of memory: Killed process 1412 (systemd) total-vm:76520kB, anon-rss:912kB, file-rss:0kB, shmem-rss:0kB
Same with the stress tool
[ 2053.102772] Out of memory: Killed process 1482 (stress) total-vm:270384kB, anon-rss:23552kB, file-rss:0kB, shmem-rss:0kB
[ 2053.148917] Out of memory: Killed process 1483 (stress) total-vm:270384kB, anon-rss:30588kB, file-rss:0kB, shmem-rss:0kB
TMEM does not seem to work on dom0
xen:tmem: frontswap enabled, RAM provided by Xen Transcendent Memory xen:tmem: cleancache enabled, RAM provided by Xen Transcendent Memory xen_selfballoon: Xen selfballooning driver disabled for domain0
Enabling Transcendent Memory https://wiki.xenproject.org/wiki/TMEM
Help! Linux ate my RAM! https://www.linuxatemyram.com/
Stress Test CPU and Memory (VM) On a Linux / Unix With Stress-ng https://www.cyberciti.biz/faq/stress-test-linux-unix-server-with-stress-ng/
Kernel same-page merging https://en.wikipedia.org/wiki/Kernel_same-page_merging