Hello there. I do not know if I should report this test to xen-devel or xen-users. In doubt I send it here, to xen-users.
Using Xen version 4.11.0 and Linux dom0 & domU 4.18.16.
I've tested the Transcendent Memory feature that seem to have been provided by Oracle. It is a success. My guests are now having dynamic memory allocation, and the shrinking is quite fast. In less that 3 minutes, it goes from 5GB to ~900MB. And after quite a while, I even goes down to less than 700MB on idling guests.
Among others, I enabled those into domU kernel (on top of x86_64_defconfig && xenconfig),
Enabling a swap space onto the guest is not mandatory. It works without swap. Also the additional `tmem` kernel argument at boot time is not required. All I had to do is to load the module once the guest is up and running.
And magic happens, its xentop MAXMEM(k) starts decreasing. It is wonderful. So, thank you Dan Magenheimer @Oracle for this great feature.
I noted that for TMEM, only the `memory=` guest setting matters. Setting `maxmem=` shows static values on xentop output. It is also interesting to note that `xl mem-set` and TMEM do not conflict in practice, although TMEM just makes the former useless. When doing `xl mem-set`, xentop shows the according amount of defined memory and then starts to drop again ^^
Beside the success report, I need to mention the few remaining issues or concerns.
I do not get why TMEM refuses to be built-in. It always converts back to a module. It is a pity because this forces me to deliver `/lib/modules/kernel-ver` onto the PV guests just for that module.
Although it just works, I cannot use the `xl` arguments relative to tmem. For example when trying `xl tmem-list`,
libxl: error: libxl_tmem.c:28:libxl_tmem_list: Domain 2:Can not get tmem list: Operation not permitted
As for the documentation, the xl(1) manual states that is needs to be done, and I found no guide to set it up. I could convert this message to some tutorial though.