[PATCH 3/7] block/qcow2: use compressed write cache

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Introduce a new option: compressed-cache-size, with default to 64
clusters (to be not less than 64 default max-workers for backup job).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 qapi/block-core.json   |  8 +++-
 block/qcow2.h          |  4 ++
 block/qcow2-refcount.c | 13 +++++++
 block/qcow2.c          | 87 ++++++++++++++++++++++++++++++++++++++++--
 4 files changed, 108 insertions(+), 4 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 9f555d5c1d..e0be6657f3 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -3202,6 +3202,11 @@
 #             an image, the data file name is loaded from the image
 #             file. (since 4.0)
 #
+# @compressed-cache-size: The maximum size of compressed write cache in
+#                         bytes. If positive must be not less than
+#                         cluster size. 0 disables the feature. Default
+#                         is 64 * cluster_size. (since 6.0)
+#
 # Since: 2.9
 ##
 { 'struct': 'BlockdevOptionsQcow2',
@@ -3217,7 +3222,8 @@
             '*refcount-cache-size': 'int',
             '*cache-clean-interval': 'int',
             '*encrypt': 'BlockdevQcow2Encryption',
-            '*data-file': 'BlockdevRef' } }
+            '*data-file': 'BlockdevRef',
+            '*compressed-cache-size': 'int' } }
 
 ##
 # @SshHostKeyCheckMode:
diff --git a/block/qcow2.h b/block/qcow2.h
index fbdedf89fa..b86aa06006 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -150,6 +150,7 @@
 #define QCOW2_OPT_L2_CACHE_ENTRY_SIZE "l2-cache-entry-size"
 #define QCOW2_OPT_REFCOUNT_CACHE_SIZE "refcount-cache-size"
 #define QCOW2_OPT_CACHE_CLEAN_INTERVAL "cache-clean-interval"
+#define QCOW2_OPT_COMPRESSED_CACHE_SIZE "compressed-cache-size"
 
 typedef struct QCowHeader {
     uint32_t magic;
@@ -422,6 +423,9 @@ typedef struct BDRVQcow2State {
      * is to convert the image with the desired compression type set.
      */
     Qcow2CompressionType compression_type;
+
+    uint64_t compressed_cache_size;
+    Qcow2CompressedWriteCache *compressed_cache;
 } BDRVQcow2State;
 
 typedef struct Qcow2COWRegion {
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 8e649b008e..5720591460 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -899,6 +899,11 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
                 qcow2_cache_discard(s->l2_table_cache, table);
             }
 
+            if (s->compressed_cache) {
+                qcow2_compressed_cache_co_discard(s->compressed_cache,
+                                                  cluster_offset);
+            }
+
             if (s->discard_passthrough[type]) {
                 update_refcount_discard(bs, cluster_offset, s->cluster_size);
             }
@@ -1110,6 +1115,14 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size)
             }
 
             if (!offset || ROUND_UP(offset, s->cluster_size) != new_cluster) {
+                if (offset && s->compressed_cache) {
+                    /*
+                     * Previous cluster is unfinished, but we'll not write more
+                     * data to it. We should inform compressed cache.
+                     */
+                    qcow2_compressed_cache_co_set_cluster_end(
+                            s->compressed_cache, offset);
+                }
                 offset = new_cluster;
                 free_in_cluster = s->cluster_size;
             } else {
diff --git a/block/qcow2.c b/block/qcow2.c
index 5d94f45be9..3997d8c143 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -808,6 +808,13 @@ static QemuOptsList qcow2_runtime_opts = {
             .type = QEMU_OPT_NUMBER,
             .help = "Clean unused cache entries after this time (in seconds)",
         },
+        {
+            .name = QCOW2_OPT_COMPRESSED_CACHE_SIZE,
+            .type = QEMU_OPT_NUMBER,
+            .help = "The maximum size of compressed write cache in bytes. If "
+                    "positive must be not less than cluster size. 0 disables "
+                    "the feature. Default is 64 * cluster_size",
+        },
         BLOCK_CRYPTO_OPT_DEF_KEY_SECRET("encrypt.",
             "ID of secret providing qcow2 AES key or LUKS passphrase"),
         { /* end of list */ }
@@ -969,6 +976,38 @@ typedef struct Qcow2ReopenState {
     QCryptoBlockOpenOptions *crypto_opts; /* Disk encryption runtime options */
 } Qcow2ReopenState;
 
+static int qcow2_update_compressed_cache_option(BlockDriverState *bs,
+                                                QemuOpts *opts, Error **errp)
+{
+    BDRVQcow2State *s = bs->opaque;
+    uint64_t new_size;
+    int ret;
+
+    new_size = qemu_opt_get_size(opts, QCOW2_OPT_COMPRESSED_CACHE_SIZE,
+                                 64 * s->cluster_size);
+    if (new_size > 0 && new_size < s->cluster_size) {
+        error_setg(errp, "compressed cache size is too small");
+        return -EINVAL;
+    }
+
+    if (s->compressed_cache && !new_size) {
+        ret = qcow2_compressed_cache_stop_flush(bs, s->compressed_cache);
+        if (ret < 0) {
+            error_report("Failed to flush the compressed write cache: %s",
+                         strerror(-ret));
+            return ret;
+        }
+        qcow2_compressed_cache_free(s->compressed_cache);
+        s->compressed_cache = NULL;
+    } else if (s->compressed_cache) {
+        qcow2_compressed_cache_set_size(s->compressed_cache, new_size);
+    }
+
+    s->compressed_cache_size = new_size;
+
+    return 0;
+}
+
 static int qcow2_update_options_prepare(BlockDriverState *bs,
                                         Qcow2ReopenState *r,
                                         QDict *options, int flags,
@@ -994,6 +1033,11 @@ static int qcow2_update_options_prepare(BlockDriverState *bs,
         goto fail;
     }
 
+    ret = qcow2_update_compressed_cache_option(bs, opts, errp);
+    if (ret < 0) {
+        goto fail;
+    }
+
     /* get L2 table/refcount block cache size from command line options */
     read_cache_sizes(bs, opts, &l2_cache_size, &l2_cache_entry_size,
                      &refcount_cache_size, &local_err);
@@ -2660,6 +2704,17 @@ static int qcow2_inactivate(BlockDriverState *bs)
                           bdrv_get_device_or_node_name(bs));
     }
 
+    if (s->compressed_cache) {
+        ret = qcow2_compressed_cache_stop_flush(bs, s->compressed_cache);
+        if (ret < 0) {
+            result = ret;
+            error_report("Failed to flush the compressed write cache: %s",
+                         strerror(-ret));
+        }
+        qcow2_compressed_cache_free(s->compressed_cache);
+        s->compressed_cache = NULL;
+    }
+
     ret = qcow2_cache_flush(bs, s->l2_table_cache);
     if (ret) {
         result = ret;
@@ -2692,6 +2747,8 @@ static void qcow2_close(BlockDriverState *bs)
         qcow2_inactivate(bs);
     }
 
+    assert(!s->compressed_cache);
+
     cache_clean_timer_del(bs);
     qcow2_cache_destroy(s->l2_table_cache);
     qcow2_cache_destroy(s->refcount_block_cache);
@@ -4539,8 +4596,14 @@ qcow2_co_pwritev_compressed_task(BlockDriverState *bs,
         goto fail;
     }
 
-    BLKDBG_EVENT(s->data_file, BLKDBG_WRITE_COMPRESSED);
-    ret = bdrv_co_pwrite(s->data_file, cluster_offset, out_len, out_buf, 0);
+    if (s->compressed_cache) {
+        ret = qcow2_compressed_cache_co_write(s->compressed_cache,
+                                              cluster_offset, out_len, out_buf);
+        out_buf = NULL;
+    } else {
+        BLKDBG_EVENT(s->data_file, BLKDBG_WRITE_COMPRESSED);
+        ret = bdrv_co_pwrite(s->data_file, cluster_offset, out_len, out_buf, 0);
+    }
     if (ret < 0) {
         goto fail;
     }
@@ -4601,6 +4664,12 @@ qcow2_co_pwritev_compressed_part(BlockDriverState *bs,
         return -EINVAL;
     }
 
+    if (!s->compressed_cache && s->compressed_cache_size) {
+        s->compressed_cache =
+            qcow2_compressed_cache_new(s->data_file, s->cluster_size,
+                                       s->compressed_cache_size);
+    }
+
     while (bytes && aio_task_pool_status(aio) == 0) {
         uint64_t chunk_size = MIN(bytes, s->cluster_size);
 
@@ -4656,7 +4725,12 @@ qcow2_co_preadv_compressed(BlockDriverState *bs,
     out_buf = qemu_blockalign(bs, s->cluster_size);
 
     BLKDBG_EVENT(bs->file, BLKDBG_READ_COMPRESSED);
-    ret = bdrv_co_pread(bs->file, coffset, csize, buf, 0);
+    if (s->compressed_cache) {
+        ret = qcow2_compressed_cache_co_read(s->compressed_cache,
+                                             coffset, csize, buf);
+    } else {
+        ret = bdrv_co_pread(bs->file, coffset, csize, buf, 0);
+    }
     if (ret < 0) {
         goto fail;
     }
@@ -4875,6 +4949,13 @@ static coroutine_fn int qcow2_co_flush_to_os(BlockDriverState *bs)
     BDRVQcow2State *s = bs->opaque;
     int ret;
 
+    if (s->compressed_cache) {
+        ret = qcow2_compressed_cache_flush(bs, s->compressed_cache);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
     qemu_co_mutex_lock(&s->lock);
     ret = qcow2_write_caches(bs);
     qemu_co_mutex_unlock(&s->lock);
-- 
2.29.2