rdma: introduce ram_handle_compressed()

This gives RDMA shared access to madvise() on the destination side
when an entire chunk is found to be zero.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Chegu Vinod <chegu_vinod@hp.com>
Tested-by: Chegu Vinod <chegu_vinod@hp.com>
Tested-by: Michael R. Hines <mrhines@us.ibm.com>
Signed-off-by: Michael R. Hines <mrhines@us.ibm.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

arch_init.c

@@ -808,6 +808,24 @@ static inline void *host_from_stream_offset(QEMUFile *f,
     return NULL;
 }
 
+/*
+ * If a page (or a whole RDMA chunk) has been
+ * determined to be zero, then zap it.
+ */
+void ram_handle_compressed(void *host, uint8_t ch, uint64_t size)
+{
+    if (ch != 0 || !is_zero_page(host)) {
+        memset(host, ch, size);
+#ifndef _WIN32
+        if (ch == 0 &&
+            (!kvm_enabled() || kvm_has_sync_mmu()) &&
+            getpagesize() <= TARGET_PAGE_SIZE) {
+            qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
+        }
+#endif
+    }
+}
+
 static int ram_load(QEMUFile *f, void *opaque, int version_id)
 {
     ram_addr_t addr;
@@ -879,16 +897,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
             }
 
             ch = qemu_get_byte(f);
-            if (ch != 0 || !is_zero_page(host)) {
-                memset(host, ch, TARGET_PAGE_SIZE);
-#ifndef _WIN32
-                if (ch == 0 &&
-                    (!kvm_enabled() || kvm_has_sync_mmu()) &&
-                    getpagesize() <= TARGET_PAGE_SIZE) {
-                    qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
-                }
-#endif
-            }
+            ram_handle_compressed(host, ch, TARGET_PAGE_SIZE);
         } else if (flags & RAM_SAVE_FLAG_PAGE) {
             void *host;
 

include/migration/migration.h

@@ -109,6 +109,8 @@ uint64_t xbzrle_mig_pages_transferred(void);
 uint64_t xbzrle_mig_pages_overflow(void);
 uint64_t xbzrle_mig_pages_cache_miss(void);
 
+void ram_handle_compressed(void *host, uint8_t ch, uint64_t size);
+
 /**
  * @migrate_add_blocker - prevent migration from proceeding
  *