mm/damon/sysfs: implement a command for updating only schemes tried total bytes

Using tried_regions/total_bytes file, users can efficiently retrieve the
total size of memory regions having specific access pattern.  However,
DAMON sysfs interface in kernel still populates all the infomration on the
tried_regions subdirectories.  That means the kernel part overhead for the
construction of tried regions directories still exists.  To remove the
overhead, implement yet another command input for 'state' DAMON sysfs
file.  Writing the input to the file makes DAMON sysfs interface to update
only the total_bytes file.

Link: https://lkml.kernel.org/r/20230802213222.109841-3-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/sysfs-common.h

@@ -47,7 +47,7 @@ void damon_sysfs_schemes_update_stats(
 
 int damon_sysfs_schemes_update_regions_start(
 		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx);
+		struct damon_ctx *ctx, bool total_bytes_only);
 
 int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx);
 

mm/damon/sysfs-schemes.c

@@ -1635,6 +1635,7 @@ void damon_sysfs_schemes_update_stats(
  */
 static struct damon_sysfs_schemes *damon_sysfs_schemes_for_damos_callback;
 static int damon_sysfs_schemes_region_idx;
+static bool damos_regions_upd_total_bytes_only;
 
 /*
  * DAMON callback that called before damos apply.  While this callback is
@@ -1664,6 +1665,9 @@ static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
 
 	sysfs_regions = sysfs_schemes->schemes_arr[schemes_idx]->tried_regions;
 	sysfs_regions->total_bytes += r->ar.end - r->ar.start;
+	if (damos_regions_upd_total_bytes_only)
+		return 0;
+
 	region = damon_sysfs_scheme_region_alloc(r);
 	list_add_tail(&region->list, &sysfs_regions->regions_list);
 	sysfs_regions->nr_regions++;
@@ -1702,10 +1706,11 @@ int damon_sysfs_schemes_clear_regions(
 /* Called from damon_sysfs_cmd_request_callback under damon_sysfs_lock */
 int damon_sysfs_schemes_update_regions_start(
 		struct damon_sysfs_schemes *sysfs_schemes,
-		struct damon_ctx *ctx)
+		struct damon_ctx *ctx, bool total_bytes_only)
 {
 	damon_sysfs_schemes_clear_regions(sysfs_schemes, ctx);
 	damon_sysfs_schemes_for_damos_callback = sysfs_schemes;
+	damos_regions_upd_total_bytes_only = total_bytes_only;
 	ctx->callback.before_damos_apply = damon_sysfs_before_damos_apply;
 	return 0;
 }

mm/damon/sysfs.c

@@ -999,6 +999,11 @@ enum damon_sysfs_cmd {
 	 * files.
 	 */
 	DAMON_SYSFS_CMD_UPDATE_SCHEMES_STATS,
+	/*
+	 * @DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES: Update
+	 * tried_regions/total_bytes sysfs files for each scheme.
+	 */
+	DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES,
 	/*
 	 * @DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS: Update schemes tried
 	 * regions
@@ -1021,6 +1026,7 @@ static const char * const damon_sysfs_cmd_strs[] = {
 	"off",
 	"commit",
 	"update_schemes_stats",
+	"update_schemes_tried_bytes",
 	"update_schemes_tried_regions",
 	"clear_schemes_tried_regions",
 };
@@ -1206,12 +1212,14 @@ static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
 {
 	struct damon_target *t, *next;
 	struct damon_sysfs_kdamond *kdamond;
+	enum damon_sysfs_cmd cmd;
 
 	/* damon_sysfs_schemes_update_regions_stop() might not yet called */
 	kdamond = damon_sysfs_cmd_request.kdamond;
-	if (kdamond && damon_sysfs_cmd_request.cmd ==
-			DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS &&
-			ctx == kdamond->damon_ctx) {
+	cmd = damon_sysfs_cmd_request.cmd;
+	if (kdamond && ctx == kdamond->damon_ctx &&
+			(cmd == DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS ||
+			 cmd == DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES)) {
 		damon_sysfs_schemes_update_regions_stop(ctx);
 		mutex_unlock(&damon_sysfs_lock);
 	}
@@ -1248,14 +1256,15 @@ static int damon_sysfs_upd_schemes_stats(struct damon_sysfs_kdamond *kdamond)
 }
 
 static int damon_sysfs_upd_schemes_regions_start(
-		struct damon_sysfs_kdamond *kdamond)
+		struct damon_sysfs_kdamond *kdamond, bool total_bytes_only)
 {
 	struct damon_ctx *ctx = kdamond->damon_ctx;
 
 	if (!ctx)
 		return -EINVAL;
 	return damon_sysfs_schemes_update_regions_start(
-			kdamond->contexts->contexts_arr[0]->schemes, ctx);
+			kdamond->contexts->contexts_arr[0]->schemes, ctx,
+			total_bytes_only);
 }
 
 static int damon_sysfs_upd_schemes_regions_stop(
@@ -1332,6 +1341,7 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c)
 {
 	struct damon_sysfs_kdamond *kdamond;
 	static bool damon_sysfs_schemes_regions_updating;
+	bool total_bytes_only = false;
 	int err = 0;
 
 	/* avoid deadlock due to concurrent state_store('off') */
@@ -1348,9 +1358,13 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c)
 	case DAMON_SYSFS_CMD_COMMIT:
 		err = damon_sysfs_commit_input(kdamond);
 		break;
+	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_BYTES:
+		total_bytes_only = true;
+		fallthrough;
 	case DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS:
 		if (!damon_sysfs_schemes_regions_updating) {
-			err = damon_sysfs_upd_schemes_regions_start(kdamond);
+			err = damon_sysfs_upd_schemes_regions_start(kdamond,
+					total_bytes_only);
 			if (!err) {
 				damon_sysfs_schemes_regions_updating = true;
 				goto keep_lock_out;