Cleanup code and move IOContext mapping to Posix, as the constants we…

… use are Poxix only. On Windows we can have a totally different way to madvise the kernel

lucene/core/src/java21/org/apache/lucene/store/MemorySegmentIndexInputProvider.java

@@ -23,8 +23,6 @@
 import java.nio.channels.FileChannel.MapMode;
 import java.nio.file.Path;
 import java.nio.file.StandardOpenOption;
-import java.util.OptionalInt;
-import org.apache.lucene.store.IOContext.Context;
 import org.apache.lucene.util.Constants;
 import org.apache.lucene.util.Unwrappable;
 
@@ -83,14 +81,6 @@ private final MemorySegment[] map(
       throw new IllegalArgumentException("File too big for chunk size: " + resourceDescription);
     }
 
-    final OptionalInt advice;
-    if (chunkSizePower < 21) {
-      // if chunk size is too small (2 MiB), disable madvise support (incorrect alignment):
-      advice = OptionalInt.empty();
-    } else {
-      advice = mapContextToMadvise(context);
-    }
-
     final long chunkSize = 1L << chunkSizePower;
 
     // we always allocate one more segments, the last one may be a 0 byte one
@@ -108,29 +98,16 @@ private final MemorySegment[] map(
       } catch (IOException ioe) {
         throw convertMapFailedIOException(ioe, resourceDescription, segSize);
       }
+      // if preload apply it without madvise.
+      // if chunk size is too small (2 MiB), disable madvise support (incorrect alignment)
       if (preload) {
         segment.load();
-      } else if (segSize > 0L && advice.isPresent()) { // not when preloading!
-        nativeAccess.madvise(segment, advice.getAsInt());
+      } else if (chunkSizePower >= 21) {
+        nativeAccess.madvise(segment, context);
       }
       segments[segNr] = segment;
       startOffset += segSize;
     }
     return segments;
   }
-
-  private OptionalInt mapContextToMadvise(IOContext context) {
-    // Merging always wins and implies sequential access, because kernel is advised to free pages
-    // after use:
-    if (context.context == Context.MERGE) {
-      return OptionalInt.of(NativeAccess.POSIX_MADV_SEQUENTIAL);
-    }
-    if (context.randomAccess) {
-      return OptionalInt.of(NativeAccess.POSIX_MADV_RANDOM);
-    }
-    if (context.readOnce) {
-      return OptionalInt.of(NativeAccess.POSIX_MADV_SEQUENTIAL);
-    }
-    return OptionalInt.empty();
-  }
 }

lucene/core/src/java21/org/apache/lucene/store/NativeAccess.java

@@ -26,25 +26,8 @@
 abstract class NativeAccess {
   private static final Logger LOG = Logger.getLogger(NativeAccess.class.getName());
 
-  // these constants were extracted from glibc and macos header files - luckily they are the same:
-
-  /** No further special treatment. */
-  public static final int POSIX_MADV_NORMAL = 0;
-
-  /** Expect random page references. */
-  public static final int POSIX_MADV_RANDOM = 1;
-
-  /** Expect sequential page references. */
-  public static final int POSIX_MADV_SEQUENTIAL = 2;
-
-  /** Will need these pages. */
-  public static final int POSIX_MADV_WILLNEED = 3;
-
-  /** Don't need these pages. */
-  public static final int POSIX_MADV_DONTNEED = 4;
-
   /** Invoke the {@code madvise} call for the given {@link MemorySegment}. */
-  public abstract void madvise(MemorySegment segment, int advice) throws IOException;
+  public abstract void madvise(MemorySegment segment, IOContext context) throws IOException;
 
   /**
    * Return the NativeAccess instance for this platform. At moment we only support Linux and MacOS

lucene/core/src/java21/org/apache/lucene/store/NoopNativeAccess.java

@@ -22,5 +22,5 @@
 final class NoopNativeAccess extends NativeAccess {
 
   @Override
-  public void madvise(MemorySegment segment, int advice) {}
+  public void madvise(MemorySegment segment, IOContext context) {}
 }

lucene/core/src/java21/org/apache/lucene/store/PosixNativeAccess.java

@@ -25,12 +25,30 @@
 import java.lang.invoke.MethodHandle;
 import java.util.Locale;
 import java.util.logging.Logger;
+import org.apache.lucene.store.IOContext.Context;
 
 @SuppressWarnings("preview")
 final class PosixNativeAccess extends NativeAccess {
 
   private static final Logger LOG = Logger.getLogger(PosixNativeAccess.class.getName());
 
+  // these constants were extracted from glibc and macos header files - luckily they are the same:
+
+  /** No further special treatment. */
+  public static final int POSIX_MADV_NORMAL = 0;
+
+  /** Expect random page references. */
+  public static final int POSIX_MADV_RANDOM = 1;
+
+  /** Expect sequential page references. */
+  public static final int POSIX_MADV_SEQUENTIAL = 2;
+
+  /** Will need these pages. */
+  public static final int POSIX_MADV_WILLNEED = 3;
+
+  /** Don't need these pages. */
+  public static final int POSIX_MADV_DONTNEED = 4;
+
   private final MethodHandle mh$posix_madvise;
 
   public PosixNativeAccess() {
@@ -62,10 +80,17 @@ private static MethodHandle findFunction(
   }
 
   @Override
-  public void madvise(MemorySegment segment, int advice) throws IOException {
+  public void madvise(MemorySegment segment, IOContext context) throws IOException {
+    if (segment.byteSize() == 0L) {
+      return; // empty segments should be excluded, because they may have no address at all
+    }
+    final Integer advice = mapIOContext(context);
+    if (advice == null) {
+      return; // do nothing
+    }
     final int ret;
     try {
-      ret = (int) mh$posix_madvise.invokeExact(segment, segment.byteSize(), advice);
+      ret = (int) mh$posix_madvise.invokeExact(segment, segment.byteSize(), advice.intValue());
     } catch (Throwable th) {
       throw new AssertionError(th);
     }
@@ -79,4 +104,19 @@ public void madvise(MemorySegment segment, int advice) throws IOException {
               ret));
     }
   }
+
+  private Integer mapIOContext(IOContext ctx) {
+    // Merging always wins and implies sequential access, because kernel is advised to free pages
+    // after use:
+    if (ctx.context == Context.MERGE) {
+      return POSIX_MADV_SEQUENTIAL;
+    }
+    if (ctx.randomAccess) {
+      return POSIX_MADV_RANDOM;
+    }
+    if (ctx.readOnce) {
+      return POSIX_MADV_SEQUENTIAL;
+    }
+    return null;
+  }
 }