Reserved System Overhead

Some necessary system components required by the pods occupy system resources. There is a difference between the memory in the pod flavor and the allocatable pod memory. CCI calculates the pod memory that can be allocated as follows:

Memory in the pod flavor ≤ 2 GiB
Allocatable pod memory = Memory in the pod flavor

Memory in the pod flavor > 2 GiB
Allocatable pod memory = Memory in the pod flavor – Memory reserved for CCI – Memory reserved for the OS

Memory in the pod flavor is the value of ${memoryCeil} displayed in the pod annotation in the format of resource.cci.io/size=${cpuCeil}_${memoryCeil}.

Rules for Reserving Pod Memory on CCI

The total reserved pod memory is equal to the sum of that reserved for the OS and that reserved for CCI to manage the pod.

The memory reserved for the OS includes basic memory and floating memory that varies with the memory in the pod flavor. The memory reserved for CCI to manage the pod is 250 MiB.

**Table 1** Rules for reserving pod memory
Scenario	Reserved for	Basic/Floating	Reservation	Used by
Memory in the pod flavor ≤ 2 GiB	None	\	\	\
Memory in the pod flavor > 2 GiB	OS	Basic	Fixed at 150 MiB	OS services
	OS	Floating reservation (varying with the memory in the pod flavor)	20 MiB per GiB	OS kernel
	CCI	Basic	Fixed at 250 MiB	CCI components

Example

**Table 2** Reservation example
Memory in the Pod Flavor	Available Pod Memory	Calculation	Remarks
0.5 GiB	0.5 GiB	/	Memory in the pod flavor ≤ 2 GiB
1 GiB	1 GiB	/
2 GiB	2 GiB	/
3 GiB	2.55 GiB	3 GiB – 250 MiB – (150 MiB + 3 × 20 MiB) = 2.55 GiB	Memory in the pod flavor > 2 GiB
4 GiB	3.53 GiB	4 GiB – 250 MiB – (150 MiB + 4 × 20 MiB) = 3.53 GiB
8 GiB	7.45 GiB	8 GiB – 250 MiB – (150 MiB + 8 × 20 MiB) = 7.45 GiB
16 GiB	15.29 GiB	16 GiB – 250 MiB – (150 MiB + 16 × 20 MiB) = 15.29 GiB
32 GiB	30.98 GiB	32 GiB – 250 MiB – (150 MiB + 32 × 20 MiB) = 30.98 GiB
64 GiB	62.35 GiB	64 GiB – 250 MiB – (150 MiB + 64 × 20 MiB) = 62.35 GiB
128 GiB	125.1 GiB	128 GiB – 250 MiB – (150 MiB + 128 × 20 MiB) = 125.1 GiB
256 GiB	250.6 GiB	256 GiB – 250 MiB – (150 MiB + 256 × 20 MiB) = 250.6 GiB