migration: stop compression to allocate and free memory frequently

Current code uses compress2() to compress memory which manages memory
internally, that causes huge memory is allocated and freed very
frequently

More worse, frequently returning memory to kernel will flush TLBs
and trigger invalidation callbacks on mmu-notification which
interacts with KVM MMU, that dramatically reduce the performance
of VM

So, we maintain the memory by ourselves and reuse it for each
compression

Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com>
Message-Id: <20180330075128.26919-3-xiaoguangrong@tencent.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 32 insertions, 7 deletions

diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index bb63c77..bafe3a0 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -658,8 +658,32 @@ uint64_t qemu_get_be64(QEMUFile *f)
     return v;
 }
 
-/* Compress size bytes of data start at p with specific compression
- * level and store the compressed data to the buffer of f.
+/* return the size after compression, or negative value on error */
+static int qemu_compress_data(z_stream *stream, uint8_t *dest, size_t dest_len,
+                              const uint8_t *source, size_t source_len)
+{
+    int err;
+
+    err = deflateReset(stream);
+    if (err != Z_OK) {
+        return -1;
+    }
+
+    stream->avail_in = source_len;
+    stream->next_in = (uint8_t *)source;
+    stream->avail_out = dest_len;
+    stream->next_out = dest;
+
+    err = deflate(stream, Z_FINISH);
+    if (err != Z_STREAM_END) {
+        return -1;
+    }
+
+    return stream->next_out - dest;
+}
+
+/* Compress size bytes of data start at p and store the compressed
+ * data to the buffer of f.
  *
  * When f is not writable, return -1 if f has no space to save the
  * compressed data.
@@ -667,9 +691,8 @@ uint64_t qemu_get_be64(QEMUFile *f)
  * do fflush first, if f still has no space to save the compressed
  * data, return -1.
  */
-
-ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
-                                  int level)
+ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream,
+                                  const uint8_t *p, size_t size)
 {
     ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
 
@@ -683,8 +706,10 @@ ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
             return -1;
         }
     }
-    if (compress2(f->buf + f->buf_index + sizeof(int32_t), (uLongf *)&blen,
-                  (Bytef *)p, size, level) != Z_OK) {
+
+    blen = qemu_compress_data(stream, f->buf + f->buf_index + sizeof(int32_t),
+                              blen, p, size);
+    if (blen < 0) {
         error_report("Compress Failed!");
         return 0;
     }