[GR-69665] Cap to 30GiB to be closer to the previous limit of 29.8GiB

Author: eregon

docs/reference-manual/native-image/BuildOutput.md

@@ -48,7 +48,7 @@ GraalVM Native Image: Generating 'helloworld' (executable)...
  - Assertions: disabled (class-specific config may apply), system assertions: disabled
 --------------------------------------------------------------------------------
 Build resources:
- - 31.00GiB of memory (49.6% of system memory, capped at 31GiB)
+ - 30.00GiB of memory (48.0% of system memory, capped at 30GiB)
  - 32 thread(s) (88.9% of 36 available processor(s), determined at start)
 [2/8] Performing analysis...  [*******]                         (3.7s @ 0.58GiB)
     2,140 types,   1,939 fields, and   8,997 methods found reachable
@@ -180,7 +180,7 @@ The memory limit and number of threads used by the build process.
 More precisely, the memory limit of the Java heap, so actual memory consumption can be higher.
 Please check the [peak RSS](#glossary-peak-rss) reported at the end of the build to understand how much memory was actually used.
 The actual memory consumption can also be lower than the limit set, as the GC only commits memory that it needs.
-By default, the build process uses the dedicated mode (which uses 85% of system memory) in containers or CI environments (when the `$CI` environment variable is set to `true`), but never more than 31GiB of memory.
+By default, the build process uses the dedicated mode (which uses 85% of system memory) in containers or CI environments (when the `$CI` environment variable is set to `true`), but never more than 30GiB of memory.
 Otherwise, it uses shared mode, which uses the available memory to avoid memory pressure on developer machines.
 If less than 8GiB of memory are available, the build process falls back to the dedicated mode.
 Therefore, consider freeing up memory if your machine is slow during a build, for example, by closing applications that you do not need.

substratevm/src/com.oracle.svm.driver/src/com/oracle/svm/driver/MemoryUtil.java

@@ -63,13 +63,13 @@ public final class MemoryUtil {
     private static final int MIN_AVAILABLE_MEMORY_THRESHOLD_GB = 8;
 
     /*
-     * Builder uses at most 31GiB to avoid disabling compressed oops (UseCompressedOops).
+     * Builder uses at most 30GiB to avoid disabling compressed oops (UseCompressedOops).
      * UseCompressedOops seems currently disabled on my machine at values > (32 GiB - 32 MiB), so we
-     * use 31 GiB to have some margin. The actual logic at
+     * use 30 GiB to have some margin. The actual logic at
      * https://github.com/openjdk/jdk/blob/jdk-26+10/src/hotspot/share/runtime/arguments.cpp#L1429
      * depends on various factors so it seems unwise to hardcode that exact limit.
      */
-    public static final long MAX_HEAP_BYTES = 31 * GiB_TO_BYTES;
+    public static final long MAX_HEAP_BYTES = 30 * GiB_TO_BYTES;
 
     public static List<String> heuristicMemoryFlags(HostFlags hostFlags, List<String> memoryFlags) {
         /*
@@ -149,7 +149,7 @@ public static Pair<Long, String> maxMemoryHeuristic(long totalMemorySize, boolea
         // Ensure max memory size does not exceed upper limit
         if (maxMemory > MAX_HEAP_BYTES) {
             maxMemory = MAX_HEAP_BYTES;
-            reason = percentageOfSystemMemoryText(maxMemory, totalMemorySize) + ", capped at 31GiB";
+            reason = percentageOfSystemMemoryText(maxMemory, totalMemorySize) + ", capped at 30GiB";
         }
 
         // Handle memory flags