writecache: support settings metadata_only and pause_writeback

Two new settings for tuning dm-writecache.

device_mapper/all.h

@@ -982,7 +982,9 @@ struct writecache_settings {
 	uint32_t fua;
 	uint32_t nofua;
 	uint32_t cleaner;
-	uint32_t max_age;
+	uint32_t max_age;         /* in milliseconds */
+	uint32_t metadata_only;
+	uint32_t pause_writeback; /* in milliseconds */
 
 	/*
 	 * Allow an unrecognized key and its val to be passed to the kernel for
@@ -1004,6 +1006,8 @@ struct writecache_settings {
 	unsigned nofua_set:1;
 	unsigned cleaner_set:1;
 	unsigned max_age_set:1;
+	unsigned metadata_only_set:1;
+	unsigned pause_writeback_set:1;
 };
 
 int dm_tree_node_add_writecache_target(struct dm_tree_node *node,

device_mapper/libdm-deptree.c

@@ -2679,6 +2679,10 @@ static int _writecache_emit_segment_line(struct dm_task *dmt,
 		count += 1;
 	if (seg->writecache_settings.max_age_set)
 		count += 2;
+	if (seg->writecache_settings.metadata_only_set)
+		count += 1;
+	if (seg->writecache_settings.pause_writeback_set)
+		count += 2;
 	if (seg->writecache_settings.new_key)
 		count += 2;
 
@@ -2730,6 +2734,14 @@ static int _writecache_emit_segment_line(struct dm_task *dmt,
 		EMIT_PARAMS(pos, " max_age %u", seg->writecache_settings.max_age);
 	}
 
+	if (seg->writecache_settings.metadata_only_set) {
+		EMIT_PARAMS(pos, " metadata_only");
+	}
+
+	if (seg->writecache_settings.pause_writeback_set) {
+		EMIT_PARAMS(pos, " pause_writeback %u", seg->writecache_settings.pause_writeback);
+	}
+
 	if (seg->writecache_settings.new_key) {
 		EMIT_PARAMS(pos, " %s %s",
 			seg->writecache_settings.new_key,

lib/metadata/writecache_manip.c

@@ -518,6 +518,14 @@ int writecache_settings_to_str_list(struct writecache_settings *settings, struct
 		if (!_writecache_setting_str_list_add("max_age", (uint64_t)settings->max_age, NULL, result, mem))
 			errors++;
 
+	if (settings->metadata_only_set)
+		if (!_writecache_setting_str_list_add("metadata_only", (uint64_t)settings->metadata_only, NULL, result, mem))
+			errors++;
+
+	if (settings->pause_writeback_set)
+		if (!_writecache_setting_str_list_add("pause_writeback", (uint64_t)settings->pause_writeback, NULL, result, mem))
+			errors++;
+
 	if (settings->new_key && settings->new_val)
 		if (!_writecache_setting_str_list_add(settings->new_key, 0, settings->new_val, result, mem))
 			errors++;

lib/writecache/writecache.c

@@ -135,6 +135,18 @@ static int _writecache_text_import(struct lv_segment *seg,
 		seg->writecache_settings.max_age_set = 1;
 	}
 
+	if (dm_config_has_node(sn, "metadata_only")) {
+		if (!dm_config_get_uint32(sn, "metadata_only", &seg->writecache_settings.metadata_only))
+			return SEG_LOG_ERROR("Unknown writecache_setting in");
+		seg->writecache_settings.metadata_only_set = 1;
+	}
+
+	if (dm_config_has_node(sn, "pause_writeback")) {
+		if (!dm_config_get_uint32(sn, "pause_writeback", &seg->writecache_settings.pause_writeback))
+			return SEG_LOG_ERROR("Unknown writecache_setting in");
+		seg->writecache_settings.pause_writeback_set = 1;
+	}
+
 	if (dm_config_has_node(sn, "writecache_setting_key")) {
 		const char *key;
 		const char *val;
@@ -207,6 +219,14 @@ static int _writecache_text_export(const struct lv_segment *seg,
 	        outf(f, "max_age = %u", seg->writecache_settings.max_age);
 	}
 
+	if (seg->writecache_settings.metadata_only_set) {
+	        outf(f, "metadata_only = %u", seg->writecache_settings.metadata_only);
+	}
+
+	if (seg->writecache_settings.pause_writeback_set) {
+	        outf(f, "pause_writeback = %u", seg->writecache_settings.pause_writeback);
+	}
+
 	if (seg->writecache_settings.new_key && seg->writecache_settings.new_val) {
 	        outf(f, "writecache_setting_key = \"%s\"",
 	                seg->writecache_settings.new_key);

man/lvmcache.7_main

@@ -340,6 +340,21 @@ perform.  If not done beforehand, the splitcache command enables the
 cleaner mode and waits for flushing to complete before detaching the
 writecache.  Adding cleaner=0 to the splitcache command will skip the
 cleaner mode, and any required flushing is performed in device suspend.
+.
+.TP
+max_age = <milliseconds>
+Specifies the maximum age of a block in milliseconds. If a block is stored in
+the cache for too long, it will be written to the underlying device and cleaned up.
+.
+.TP
+metadata_only = 0|1
+Only metadata is promoted to the cache. This option improves performance for
+heavier REQ_META workloads.
+.
+.TP
+pause_writeback = <milliseconds>
+Pause writeback if there was some write I/O redirected to the origin volume in
+the last number of milliseconds.
 
 .SS dm-writecache using metadata profiles
 .

tools/lvchange.c

@@ -665,6 +665,16 @@ static int _lvchange_writecache(struct cmd_context *cmd,
 		seg->writecache_settings.max_age = settings.max_age;
 		set_count++;
 	}
+	if (settings.metadata_only_set) {
+		seg->writecache_settings.metadata_only_set = settings.metadata_only_set;
+		seg->writecache_settings.metadata_only = settings.metadata_only;
+		set_count++;
+	}
+	if (settings.pause_writeback_set) {
+		seg->writecache_settings.pause_writeback_set = settings.pause_writeback_set;
+		seg->writecache_settings.pause_writeback = settings.pause_writeback;
+		set_count++;
+	}
 	if (settings.new_key && settings.new_val) {
 		seg->writecache_settings.new_key = settings.new_key;
 		seg->writecache_settings.new_val = settings.new_val;

tools/toollib.c

@@ -1473,6 +1473,20 @@ static int _get_one_writecache_setting(struct cmd_context *cmd, struct writecach
 		return 1;
 	}
 
+	if (!strncmp(key, "metadata_only", strlen("metadata_only"))) {
+		if (sscanf(val, "%u", &settings->metadata_only) != 1)
+			goto_bad;
+		settings->metadata_only_set = 1;
+		return 1;
+	}
+
+	if (!strncmp(key, "pause_writeback", strlen("pause_writeback"))) {
+		if (sscanf(val, "%u", &settings->pause_writeback) != 1)
+			goto_bad;
+		settings->pause_writeback_set = 1;
+		return 1;
+	}
+
 	if (settings->new_key) {
 		log_error("Setting %s is not recognized. Only one unrecognized setting is allowed.", key);
 		return 0;