[ML] Uplift model memory limit on job migration (#37125)

When a 6.1-6.3 job is opened in a later version
we increase the model memory limit by 30% if it's
below 0.5GB. The migration of jobs from cluster
state to the config index changes the job version,
so we need to also do this uplift as part of that
config migration.

Relates #36961

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlConfigMigrator.java

@@ -37,6 +37,7 @@
 import org.elasticsearch.xpack.core.ml.MlMetadata;
 import org.elasticsearch.xpack.core.ml.MlTasks;
 import org.elasticsearch.xpack.core.ml.datafeed.DatafeedConfig;
+import org.elasticsearch.xpack.core.ml.job.config.AnalysisLimits;
 import org.elasticsearch.xpack.core.ml.job.config.Job;
 import org.elasticsearch.xpack.core.ml.job.persistence.AnomalyDetectorsIndex;
 import org.elasticsearch.xpack.core.ml.job.persistence.ElasticsearchMappings;
@@ -403,11 +404,23 @@ public static Job updateJobForMigration(Job job) {
         Map<String, Object> custom = job.getCustomSettings() == null ? new HashMap<>() : new HashMap<>(job.getCustomSettings());
         custom.put(MIGRATED_FROM_VERSION, job.getJobVersion());
         builder.setCustomSettings(custom);
+        // Increase the model memory limit for 6.1 - 6.3 jobs
+        Version jobVersion = job.getJobVersion();
+        if (jobVersion != null && jobVersion.onOrAfter(Version.V_6_1_0) && jobVersion.before(Version.V_6_3_0)) {
+            // Increase model memory limit if < 512MB
+            if (job.getAnalysisLimits() != null && job.getAnalysisLimits().getModelMemoryLimit() != null &&
+                    job.getAnalysisLimits().getModelMemoryLimit() < 512L) {
+                long updatedModelMemoryLimit = (long) (job.getAnalysisLimits().getModelMemoryLimit() * 1.3);
+                AnalysisLimits limits = new AnalysisLimits(updatedModelMemoryLimit,
+                        job.getAnalysisLimits().getCategorizationExamplesLimit());
+                builder.setAnalysisLimits(limits);
+            }
+        }
         // Pre v5.5 (ml beta) jobs do not have a version.
         // These jobs cannot be opened, we rely on the missing version
         // to indicate this.
         // See TransportOpenJobAction.validate()
-        if (job.getJobVersion() != null) {
+        if (jobVersion != null) {
             builder.setJobVersion(Version.CURRENT);
         }
         return builder.build();

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/30_ml_jobs_crud.yml

@@ -52,10 +52,6 @@ setup:
 
 ---
 "Test model memory limit is updated":
-  - skip:
-      version: "all"
-      reason: "@AwaitsFix: https://github.com/elastic/elasticsearch/issues/36961"
-
 # Jobs created in 6.1.x and 6.2.x underestimated the necessary model memory
 # limit, check the limit has been updated.
 # Opening the job updates the limit