The document summarizes a BHyVe hackathon where the goal was to implement a vmmls program to display a list of virtual machines. The participant implemented vmmls and it shows the list of VMs and available memory. Calculating available memory was challenging due to the minimal memory management in BHyVe. The participant added a new function to estimate free memory and exposed it via new ioctl calls and libvmmapi functions. Future work includes refactoring the ioctl interface and adding more features to vmmls.

1. BHyVe Hackathon
Activity Summary
©2003 Project TIMEMACHINE
BHyVe Hackathon
July 29, 2012
Takeshi HASEGAWA
[ja] @hasegaw / [en] @hasegaw_en

2. Summary
Goal
• Implement vmmls program to display the list of
virtual machines
Result
• Implemented vmmls
• It also shows available memory
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3. vmmls example
3

4. vmmls
• How
– Originally I tried to modify ls
– it was too rich, so finally I decided to write from scrach.
• What it does
– List the virtual machines
• no considerable difficulties here
– Show amount of available memory
• Oh my god...
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5. Reporting available memory
• I wanted to show how much memory available.
• src/sys/amd64/vmm/vmm_mem.c has the avail
memory pool which manages memory regions
• vmm_mem_steal_memory()
– Add available memory on physical machine
to the memory pool
• vmm_mem_alloc(size_t size);
– Allocate memory to virtual machines
from the memory pool
• vmm_mem_free(vm_paddr_t start, size_t size);
– Return allocated memory
to the memory pool
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6. Reporting available memory(cont.)
• BHyVe-sensei, I have a problem...
• The memory management is really minimum
• No one knows the amount of free memory!
• Calculated the amount of free memory
– Added new function in vmm_mem.c
– Calculates the sum of length of available memory
segments
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7. Reporting available memory(cont.)
#define VMM_MEM_MAXSEGS 64
/* protected by vmm_mem_mtx */
static struct {
vm_paddr_t base;
vm_size_t length;
} vmm_mem_avail[VMM_MEM_MAXSEGS];
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8. Reporting available memory(cont.)
Host-Physical Memory
(not used by FreeBSD)
steal
vmm_mem_avail
allo ain
allo ain
allo ain
c
recl c
recl c
recl
Guest A
Guest B
Guest C
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9. Reporting available memory(cont.)
• Added the function to estimate available memory
– vmm_mem.c (in vmm.ko)
• Added a new ioctl to allow access from userland
– VM_GET_FREEMEM
– vmm_dev.c … added a new ioctl implementation
– vmm_dev.h … added a new ioctl definition
• Added a new function to libvmmapi
– vmmapi.c … added a new function API to get available
memory amount
• Enhanced vmmls command by using the new API
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10. Again,,,
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11. Future work - 1
• Refactor the Ioctl() interface for
VM_GET_FREEMEM
– ioctl() access for vmm.ko is available only when one or
more VMs exist
– Ioctl(*, VM_GET_FREEMEM, ...) doesn t work
when no VMs exists!
• More fancy APIs
– sysctl
• Good for reporting integer value
• Is it possible to read-callback handler?
– ioctl using another special file ‒ such as /dev/bhyve
• sysctl can handle only one value
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12. Future work - 2
• Review the fields shown by vmmls command
– Number of vCPUs
– Disk files the VM is opening
– Networks
– Time
• How much CPU time the VM consumed?
– Memory status
• I m sure what lowmem and highmem means...
– Event counters?
• Such as counter of VMEXIT...
• Another program, such as vmmstat should be more better
– etc etc
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