Make Linux memory allocations int64 not uint64

The kernel ABI to these values is a string, which accepts the value `-1`
to mean "unlimited" or an integer up to 2^63 for an amount of memory in
bytes.

While the internal representation in the kernel is unsigned, this is not
exposed in any ABI directly. Because of the user-kernel memory split, values
over 2^63 are not really useful; indeed that much memory is not supported,
as physical memory is limited to 52 bits in the forthcoming switch to five
level page tables. So it is much more natural to support the value `-1` for
unlimited, especially as the actual number needed to represent the maximum
has varied in different kernel versions, and across 32 and 64 bit architectures,
so determining the value to use is not possible, so it is necessary to write
the string `-1` to the cgroup files.

See also discussion in
- opencontainers/runc#1494
- opencontainers/runc#1492
- opencontainers/runc#1375
- opencontainers/runc#1421

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

config-linux.md

@@ -270,13 +270,16 @@ For more information, see the kernel cgroups documentation about [memory][cgroup
 **`memory`** (object, OPTIONAL) represents the cgroup subsystem `memory` and it's used to set limits on the container's memory usage.
 For more information, see the kernel cgroups documentation about [memory][cgroup-v1-memory].
 
+Values specify the limit in bytes, or `-1` for unlimited memory. For `swappiness` the values are from `0` (almost never swap) to `100`
+(very likely to be swapped).
+
 The following parameters can be specified to set up the controller:
 
-* **`limit`** *(uint64, OPTIONAL)* - sets limit of memory usage in bytes
-* **`reservation`** *(uint64, OPTIONAL)* - sets soft limit of memory usage in bytes
-* **`swap`** *(uint64, OPTIONAL)* - sets limit of memory+Swap usage
-* **`kernel`** *(uint64, OPTIONAL)* - sets hard limit for kernel memory
-* **`kernelTCP`** *(uint64, OPTIONAL)* - sets hard limit in bytes for kernel TCP buffer memory
+* **`limit`** *(int64, OPTIONAL)* - sets limit of memory usage in bytes
+* **`reservation`** *(int64, OPTIONAL)* - sets soft limit of memory usage in bytes
+* **`swap`** *(int64, OPTIONAL)* - sets limit of memory+Swap usage
+* **`kernel`** *(int64, OPTIONAL)* - sets hard limit for kernel memory
+* **`kernelTCP`** *(int64, OPTIONAL)* - sets hard limit in bytes for kernel TCP buffer memory
 * **`swappiness`** *(uint64, OPTIONAL)* - sets swappiness parameter of vmscan (See sysctl's vm.swappiness)
 
 #### Example

schema/config-linux.json

@@ -172,23 +172,23 @@
                         "properties": {
                             "kernel": {
                                 "id": "https://opencontainers.org/schema/bundle/linux/resources/memory/kernel",
-                                "$ref": "defs.json#/definitions/uint64"
+                                "$ref": "defs.json#/definitions/int64"
                             },
                             "kernelTCP": {
                                 "id": "https://opencontainers.org/schema/bundle/linux/resources/memory/kernelTCP",
-                                "$ref": "defs.json#/definitions/uint64"
+                                "$ref": "defs.json#/definitions/int64"
                             },
                             "limit": {
                                 "id": "https://opencontainers.org/schema/bundle/linux/resources/memory/limit",
-                                "$ref": "defs.json#/definitions/uint64"
+                                "$ref": "defs.json#/definitions/int64"
                             },
                             "reservation": {
                                 "id": "https://opencontainers.org/schema/bundle/linux/resources/memory/reservation",
-                                "$ref": "defs.json#/definitions/uint64"
+                                "$ref": "defs.json#/definitions/int64"
                             },
                             "swap": {
                                 "id": "https://opencontainers.org/schema/bundle/linux/resources/memory/swap",
-                                "$ref": "defs.json#/definitions/uint64"
+                                "$ref": "defs.json#/definitions/int64"
                             },
                             "swappiness": {
                                 "id": "https://opencontainers.org/schema/bundle/linux/resources/memory/swappiness",

specs-go/config.go

@@ -273,15 +273,15 @@ type LinuxBlockIO struct {
 // LinuxMemory for Linux cgroup 'memory' resource management
 type LinuxMemory struct {
 	// Memory limit (in bytes).
-	Limit *uint64 `json:"limit,omitempty"`
+	Limit *int64 `json:"limit,omitempty"`
 	// Memory reservation or soft_limit (in bytes).
-	Reservation *uint64 `json:"reservation,omitempty"`
+	Reservation *int64 `json:"reservation,omitempty"`
 	// Total memory limit (memory + swap).
-	Swap *uint64 `json:"swap,omitempty"`
+	Swap *int64 `json:"swap,omitempty"`
 	// Kernel memory limit (in bytes).
-	Kernel *uint64 `json:"kernel,omitempty"`
+	Kernel *int64 `json:"kernel,omitempty"`
 	// Kernel memory limit for tcp (in bytes)
-	KernelTCP *uint64 `json:"kernelTCP,omitempty"`
+	KernelTCP *int64 `json:"kernelTCP,omitempty"`
 	// How aggressive the kernel will swap memory pages.
 	Swappiness *uint64 `json:"swappiness,omitempty"`
 }