+#ifndef MADV_REMOVE
+#define MADV_REMOVE KERNEL_MADV_REMOVE
+#endif
+
+int os_drop_memory(void *addr, int length)
+{
+ int err;
+
+ err = madvise(addr, length, MADV_REMOVE);
+ if(err < 0)
+ err = -errno;
+ return err;
+}
+
+int can_drop_memory(void)
+{
+ void *addr;
+ int fd, ok = 0;
+
+ printk("Checking host MADV_REMOVE support...");
+ fd = create_mem_file(UM_KERN_PAGE_SIZE);
+ if(fd < 0){
+ printk("Creating test memory file failed, err = %d\n", -fd);
+ goto out;
+ }
+
+ addr = mmap64(NULL, UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
+ MAP_SHARED, fd, 0);
+ if(addr == MAP_FAILED){
+ printk("Mapping test memory file failed, err = %d\n", -errno);
+ goto out_close;
+ }
+
+ if(madvise(addr, UM_KERN_PAGE_SIZE, MADV_REMOVE) != 0){
+ printk("MADV_REMOVE failed, err = %d\n", -errno);
+ goto out_unmap;
+ }
+
+ printk("OK\n");
+ ok = 1;
+
+out_unmap:
+ munmap(addr, UM_KERN_PAGE_SIZE);
+out_close:
+ close(fd);
+out:
+ return ok;
+}
+