Mathieu Benoit
7199a7cbb2
La profondeur d'imbrication praticable ne se déduit pas, elle se mesure. Une mesure à la main a trouvé, au quatrième étage, un invité 36 fois plus lent que le temps réel — 583 secondes d'horloge pour 16 secondes de temps invité, chaque ligne d'ACPI prenant une seconde — puis un noyau gelé au MÊME octet quelles que soient les ressources. Un chiffre obtenu une fois, sur une machine, n'est pas un chiffre. D'où trois choses. L'algorithme, en fonctions pures. Deux ressources s'épuisent en descendant : la mémoire, chaque étage gardant de quoi faire tourner ses propres démons, et le disque, celui de l'enfant vivant DANS celui du parent. Une troisième se dégrade, et elle borne le vCPU à deux au-delà du premier étage : douze ont gelé le noyau invité, les mêmes deux avançaient. La mémoire n'est PAS bornée — la même VM gelait au même octet avec 9 Go et avec 2 Go, donc la rogner ne gagnerait rien et priverait l'étage du dessous. Le plan est annoncé avant toute création, et jamais au-delà de ce qui tient. Le garde-fou dans l'écran. Il lisait la capacité de l'HÔTE et l'offrait en entier : sur un troisième étage à 14 cœurs, il a proposé 12 vCPU à une VM qui n'a jamais démarré. Le nombre n'était pas absurde pour la machine ; il l'était pour sa profondeur, que l'écran ignorait. Elle se compte maintenant sur la chaîne de ProxyJump — un rebond par étage, et c'est nous qui écrivons ces entrées. Le test long, dans LongTest/ et non dans test/ : le lanceur unitaire doit rester lançable en quelques secondes, partout, y compris sans virtualisation. La descente est uniforme — créer, attendre le ssh, installer, redémarrer et vérifier le noyau, remettre pmxcfs debout, contrôler le stockage — et s'arrête au premier étage qui échoue en NOMMANT l'étape. Il envoie notre install_proxmox.sh par scp plutôt que de laisser la VM cloner le dépôt : c'est notre code qu'on éprouve, et un correctif absent du distant a fait revenir le même défaut sur trois VM. --- EN --- The practicable nesting depth cannot be deduced, only measured. A manual measurement found, at the fourth level, a guest 36 times slower than real time — 583 seconds of wall clock for 16 seconds of guest time, each ACPI line taking a second — then a kernel frozen at the SAME byte whatever the resources. A number obtained once, on one machine, is not a number. Hence three things. The algorithm, in pure functions. Two resources run out going down: memory, each level keeping what its own daemons need, and disk, the child's living INSIDE the parent's. A third degrades, and it caps the vCPU at two beyond the first level: twelve froze the guest kernel, the same two progressed. Memory is NOT capped — the same VM froze at the same byte with 9 GB and with 2 GB, so trimming it would gain nothing and starve the level below. The plan is announced before anything is created, and never beyond what fits. The guard in the screen. It read the HOST's capacity and offered all of it: on a third level with 14 cores it proposed 12 vCPU to a VM that never booted. The number was not absurd for the machine; it was for its depth, which the screen did not know. It is now counted on the ProxyJump chain — one hop per level, and we are the ones writing those entries. The long test, in LongTest/ and not test/: the unit runner must stay runnable in seconds, anywhere, including without virtualisation. The descent is uniform — create, wait for ssh, install, reboot and check the kernel, bring pmxcfs back, check the storage — and stops at the first level that fails, NAMING the step. It sends our install_proxmox.sh over scp instead of letting the VM clone the repository: it is our code being exercised, and a fix absent from the remote made the same defect return on three VMs. Assisted-by: Claude Opus 5 (cherry picked from commit 4f70c461330cac6f46783a60e0f33052a979fa23)
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LongTest — tests that create real machines
These are not unit tests. They create virtual machines, install systems on
them, and take hours. They live here and not in test/, which the unit
runner sweeps: ./script/test/run_unit_test.sh must stay runnable in seconds
on any machine, including one without virtualisation.
Run them from the menu — TODO › Execute › Test › Long tests — or directly.
deep_proxmox.py — how deep does Proxmox-in-Proxmox go?
The practicable nesting depth cannot be deduced, only measured. A manual measurement found, at the fourth level, a guest 36 times slower than real time — 583 seconds of wall clock for 16 seconds of guest time, each ACPI line taking a second — then a guest kernel frozen at the same byte whatever the resources. A number obtained once, on one machine, is not a number: this script redoes it on demand and says exactly where it breaks.
./LongTest/deep_proxmox.py --depth 10 --dry-run # the plan, nothing created
./LongTest/deep_proxmox.py --depth 10 # hours
./LongTest/deep_proxmox.py --detruire # undo it
The descent is uniform. Every level, the first included, goes through the
same six steps: create, wait for ssh, install Proxmox, reboot and check the
kernel, bring pmxcfs back up, check the storage. Only creation differs —
libvirt locally, qm afterwards.
It sends our install_proxmox.sh over scp instead of letting the VM clone
the repository: it is our code we want to exercise, and the remote is often
behind the checkout — a fix absent from the remote made the same defect "come
back" on three VMs in a row.
The resource algorithm
Two things run out going down, and a third degrades. What runs out is
arithmetic, and script/proxmox/nesting.py computes it:
- memory — each level keeps what its own daemons need (
pve-cluster,pvestatd,pvedaemon,pveproxy) before handing the rest down; - disk — the child's disk lives inside the parent's, which must also hold its own system.
What degrades is measured, not assumed: past the second level, vendors document nothing. Hence one capped number — 2 vCPU for every nested level. Twelve vCPU at the fourth level froze the guest kernel in early boot; the same two progressed. Bringing twelve processors online costs as many round trips through the whole stack.
Memory is not capped: the same VM froze at the same byte with 9 GB and with 2 GB, so trimming it would gain nothing and starve the level below.
The plan is printed before anything is created, and the script never promises a depth it knows will not fit — better to announce six levels and reach six than to promise ten and die at the seventh without knowing why.