Improve flushing pagecache on darwin

configure

@@ -2997,7 +2997,6 @@ fi
 print_config "timerfd_create" "$timerfd_create"
 
 #############################################################################
-
 if test "$wordsize" = "64" ; then
   output_sym "CONFIG_64BIT"
 elif test "$wordsize" = "32" ; then

helpers.c

@@ -26,9 +26,19 @@ int sync_file_range(int fd, uint64_t offset, uint64_t nbytes,
 }
 #endif
 
+#if defined (__APPLE__)
+int posix_fadvise(int fd, off_t offset, off_t len, int advice)
+{
+	if (advice == POSIX_FADV_DONTNEED)
+		return discard_pages(fd, offset, len);
+        errno = EINVAL; 
+	return -1;
+}
+#else
 #ifndef CONFIG_POSIX_FADVISE
 int posix_fadvise(int fd, off_t offset, off_t len, int advice)
 {
 	return 0;
 }
 #endif
+#endif /* defined (__APPLE__) */

os/os-mac.h

@@ -14,6 +14,11 @@
 #include <machine/endian.h>
 #include <libkern/OSByteOrder.h>
 
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <stdio.h>
+
+
 #include "../arch/arch.h"
 #include "../file.h"
 
@@ -117,3 +122,60 @@ static inline bool os_cpu_has(cpu_features feature)
 }
 
 #endif
+
+#if defined (__APPLE__)
+/*
+ * discard_pages should not be run within Rosetta. Native arm64 or x86 only. 
+ */
+
+#define MMAP_CHUNK_SIZE		(1024 * 1024 * 1024)
+
+static inline int discard_pages(int fd, off_t offset, off_t size)
+{
+	caddr_t *addr;
+	uint64_t chunk_size = MMAP_CHUNK_SIZE;
+
+	if (fsync(fd) < 0) {
+                int __err = errno; 
+		fprintf(stderr, "Cannot fsync file\n");
+                errno = __err;
+		return -1;
+	}	    
+
+	/*
+	 * mmap the file in 1GB chunks and msync(MS_INVALIDATE).
+	 */
+	while (size > 0) {
+		uint64_t mmap_size = MIN(chunk_size, size);
+
+		addr = mmap((caddr_t)0, mmap_size, PROT_NONE, MAP_SHARED, fd, offset);
+		if (addr == MAP_FAILED) {
+                        int __map_errno = errno;
+			fprintf(stderr, "Failed to mmap (%s), offset = %llu, size = %llu\n",
+				strerror(errno), offset, mmap_size);
+                        errno = __map_errno;
+			return -1;
+		}
+
+		if (msync(addr, mmap_size, MS_INVALIDATE)) {
+                        int __msync_errno = errno;
+			fprintf(stderr, "msync failed to free cache pages.\n");
+                        errno = __msync_errno;
+			return -1;
+		}
+
+		/* Destroy the above mappings used to invalidate cache - cleaning up */
+		if (munmap(addr, mmap_size) < 0) {
+                        int __munmap_errno = errno;
+			fprintf(stderr, "munmap failed, error = %d.\n", errno);
+                        errno = __munmap_errno;
+			return -1;
+		}
+
+		size -= mmap_size;
+		offset += mmap_size;
+	}
+
+	return 0;
+}
+#endif /* defined (__APPLE__) */