DRA API: bump maximum size of ReservedFor to 256

The original limit of 32 seemed sufficient for a single GPU on a node. But for
shared non-local resources it is too low. For example, a ResourceClaim might be
used to allocate an interconnect channel that connects all pods of a workload
running on several different nodes, in which case the number of pods can be
considerably larger.

256 is high enough for currently planned systems. If we need something even
higher in the future, an alternative approach might be needed to avoid
scalability problems.

Normally, increasing such a limit would have to be done incrementally over two
releases. In this case we decided on
Slack (https://kubernetes.slack.com/archives/CJUQN3E4T/p1734593174791519) to
make an exception and apply this change to current master for 1.33 and backport
it to the next 1.32.x patch release for production usage.

This breaks downgrades to a 1.32 release without this change if there are
ResourceClaims with a number of consumers > 32 in ReservedFor. In practice,
this breakage is very unlikely because there are no workloads yet which need so
many consumers and such downgrades to a previous patch release are also
unlikely. Downgrades to 1.31 already weren't supported when using DRA v1beta1.

Kubernetes-commit: 1cee3682da944f36ee9a3655bface4ff572d416e

resource/v1alpha3/types.go

@@ -687,7 +687,7 @@ type ResourceClaimStatus struct {
 	// which issued it knows that it must put the pod back into the queue,
 	// waiting for the ResourceClaim to become usable again.
 	//
-	// There can be at most 32 such reservations. This may get increased in
+	// There can be at most 256 such reservations. This may get increased in
 	// the future, but not reduced.
 	//
 	// +optional
@@ -715,9 +715,9 @@ type ResourceClaimStatus struct {
 	Devices []AllocatedDeviceStatus `json:"devices,omitempty" protobuf:"bytes,4,opt,name=devices"`
 }
 
-// ReservedForMaxSize is the maximum number of entries in
+// ResourceClaimReservedForMaxSize is the maximum number of entries in
 // claim.status.reservedFor.
-const ResourceClaimReservedForMaxSize = 32
+const ResourceClaimReservedForMaxSize = 256
 
 // ResourceClaimConsumerReference contains enough information to let you
 // locate the consumer of a ResourceClaim. The user must be a resource in the same

resource/v1alpha3/types_swagger_doc_generated.go

@@ -291,7 +291,7 @@ func (ResourceClaimSpec) SwaggerDoc() map[string]string {
 var map_ResourceClaimStatus = map[string]string{
 	"":            "ResourceClaimStatus tracks whether the resource has been allocated and what the result of that was.",
 	"allocation":  "Allocation is set once the claim has been allocated successfully.",
-	"reservedFor": "ReservedFor indicates which entities are currently allowed to use the claim. A Pod which references a ResourceClaim which is not reserved for that Pod will not be started. A claim that is in use or might be in use because it has been reserved must not get deallocated.\n\nIn a cluster with multiple scheduler instances, two pods might get scheduled concurrently by different schedulers. When they reference the same ResourceClaim which already has reached its maximum number of consumers, only one pod can be scheduled.\n\nBoth schedulers try to add their pod to the claim.status.reservedFor field, but only the update that reaches the API server first gets stored. The other one fails with an error and the scheduler which issued it knows that it must put the pod back into the queue, waiting for the ResourceClaim to become usable again.\n\nThere can be at most 32 such reservations. This may get increased in the future, but not reduced.",
+	"reservedFor": "ReservedFor indicates which entities are currently allowed to use the claim. A Pod which references a ResourceClaim which is not reserved for that Pod will not be started. A claim that is in use or might be in use because it has been reserved must not get deallocated.\n\nIn a cluster with multiple scheduler instances, two pods might get scheduled concurrently by different schedulers. When they reference the same ResourceClaim which already has reached its maximum number of consumers, only one pod can be scheduled.\n\nBoth schedulers try to add their pod to the claim.status.reservedFor field, but only the update that reaches the API server first gets stored. The other one fails with an error and the scheduler which issued it knows that it must put the pod back into the queue, waiting for the ResourceClaim to become usable again.\n\nThere can be at most 256 such reservations. This may get increased in the future, but not reduced.",
 	"devices":     "Devices contains the status of each device allocated for this claim, as reported by the driver. This can include driver-specific information. Entries are owned by their respective drivers.",
 }
 

resource/v1beta1/types.go

@@ -695,7 +695,7 @@ type ResourceClaimStatus struct {
 	// which issued it knows that it must put the pod back into the queue,
 	// waiting for the ResourceClaim to become usable again.
 	//
-	// There can be at most 32 such reservations. This may get increased in
+	// There can be at most 256 such reservations. This may get increased in
 	// the future, but not reduced.
 	//
 	// +optional
@@ -723,9 +723,9 @@ type ResourceClaimStatus struct {
 	Devices []AllocatedDeviceStatus `json:"devices,omitempty" protobuf:"bytes,4,opt,name=devices"`
 }
 
-// ReservedForMaxSize is the maximum number of entries in
+// ResourceClaimReservedForMaxSize is the maximum number of entries in
 // claim.status.reservedFor.
-const ResourceClaimReservedForMaxSize = 32
+const ResourceClaimReservedForMaxSize = 256
 
 // ResourceClaimConsumerReference contains enough information to let you
 // locate the consumer of a ResourceClaim. The user must be a resource in the same

resource/v1beta1/types_swagger_doc_generated.go

@@ -300,7 +300,7 @@ func (ResourceClaimSpec) SwaggerDoc() map[string]string {
 var map_ResourceClaimStatus = map[string]string{
 	"":            "ResourceClaimStatus tracks whether the resource has been allocated and what the result of that was.",
 	"allocation":  "Allocation is set once the claim has been allocated successfully.",
-	"reservedFor": "ReservedFor indicates which entities are currently allowed to use the claim. A Pod which references a ResourceClaim which is not reserved for that Pod will not be started. A claim that is in use or might be in use because it has been reserved must not get deallocated.\n\nIn a cluster with multiple scheduler instances, two pods might get scheduled concurrently by different schedulers. When they reference the same ResourceClaim which already has reached its maximum number of consumers, only one pod can be scheduled.\n\nBoth schedulers try to add their pod to the claim.status.reservedFor field, but only the update that reaches the API server first gets stored. The other one fails with an error and the scheduler which issued it knows that it must put the pod back into the queue, waiting for the ResourceClaim to become usable again.\n\nThere can be at most 32 such reservations. This may get increased in the future, but not reduced.",
+	"reservedFor": "ReservedFor indicates which entities are currently allowed to use the claim. A Pod which references a ResourceClaim which is not reserved for that Pod will not be started. A claim that is in use or might be in use because it has been reserved must not get deallocated.\n\nIn a cluster with multiple scheduler instances, two pods might get scheduled concurrently by different schedulers. When they reference the same ResourceClaim which already has reached its maximum number of consumers, only one pod can be scheduled.\n\nBoth schedulers try to add their pod to the claim.status.reservedFor field, but only the update that reaches the API server first gets stored. The other one fails with an error and the scheduler which issued it knows that it must put the pod back into the queue, waiting for the ResourceClaim to become usable again.\n\nThere can be at most 256 such reservations. This may get increased in the future, but not reduced.",
 	"devices":     "Devices contains the status of each device allocated for this claim, as reported by the driver. This can include driver-specific information. Entries are owned by their respective drivers.",
 }