mm/damon/sysfs-schemes: implement DAMOS-tried regions clear command

When there are huge number of DAMON regions that specific scheme actions
are tried to be applied, directories and files under 'tried_regions'
scheme directory could waste some memory.  Add another special input
keyword ('clear_schemes_tried_regions') for 'state' file of each kdamond
sysfs directory that can be used for cleanup of the 'tried_regions'
sub-directories.

[sj@kernel.org: skip regions clearing if the scheme directory was removed]
  Link: https://lkml.kernel.org/r/20221114182954.4745-3-sj@kernel.org
Link: https://lkml.kernel.org/r/20221101220328.95765-6-sj@kernel.org
Signed-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

@@ -50,3 +50,7 @@ int damon_sysfs_schemes_update_regions_start(
 		struct damon_ctx *ctx);
 
 int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx);
+
+int damon_sysfs_schemes_clear_regions(
+		struct damon_sysfs_schemes *sysfs_schemes,
+		struct damon_ctx *ctx);

mm/damon/sysfs-schemes.c

@@ -1292,7 +1292,7 @@ static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
 }
 
 /* Called from damon_sysfs_cmd_request_callback under damon_sysfs_lock */
-int damon_sysfs_schemes_update_regions_start(
+int damon_sysfs_schemes_clear_regions(
 		struct damon_sysfs_schemes *sysfs_schemes,
 		struct damon_ctx *ctx)
 {
@@ -1302,11 +1302,23 @@ int damon_sysfs_schemes_update_regions_start(
 	damon_for_each_scheme(scheme, ctx) {
 		struct damon_sysfs_scheme *sysfs_scheme;
 
+		/* user could have removed the scheme sysfs dir */
+		if (schemes_idx >= sysfs_schemes->nr)
+			break;
+
 		sysfs_scheme = sysfs_schemes->schemes_arr[schemes_idx++];
 		damon_sysfs_scheme_regions_rm_dirs(
 				sysfs_scheme->tried_regions);
 	}
+	return 0;
+}
 
+/* 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)
+{
+	damon_sysfs_schemes_clear_regions(sysfs_schemes, ctx);
 	damon_sysfs_schemes_for_damos_callback = sysfs_schemes;
 	ctx->callback.before_damos_apply = damon_sysfs_before_damos_apply;
 	return 0;

mm/damon/sysfs.c

@@ -1004,6 +1004,11 @@ enum damon_sysfs_cmd {
 	 * regions
 	 */
 	DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS,
+	/*
+	 * @DAMON_SYSFS_CMD_CLEAR_SCHEMES_TRIED_REGIONS: Clear schemes tried
+	 * regions
+	 */
+	DAMON_SYSFS_CMD_CLEAR_SCHEMES_TRIED_REGIONS,
 	/*
 	 * @NR_DAMON_SYSFS_CMDS: Total number of DAMON sysfs commands.
 	 */
@@ -1017,6 +1022,7 @@ static const char * const damon_sysfs_cmd_strs[] = {
 	"commit",
 	"update_schemes_stats",
 	"update_schemes_tried_regions",
+	"clear_schemes_tried_regions",
 };
 
 /*
@@ -1262,6 +1268,17 @@ static int damon_sysfs_upd_schemes_regions_stop(
 	return damon_sysfs_schemes_update_regions_stop(ctx);
 }
 
+static int damon_sysfs_clear_schemes_regions(
+		struct damon_sysfs_kdamond *kdamond)
+{
+	struct damon_ctx *ctx = kdamond->damon_ctx;
+
+	if (!ctx)
+		return -EINVAL;
+	return damon_sysfs_schemes_clear_regions(
+			kdamond->contexts->contexts_arr[0]->schemes, ctx);
+}
+
 static inline bool damon_sysfs_kdamond_running(
 		struct damon_sysfs_kdamond *kdamond)
 {
@@ -1343,6 +1360,9 @@ static int damon_sysfs_cmd_request_callback(struct damon_ctx *c)
 			damon_sysfs_schemes_regions_updating = false;
 		}
 		break;
+	case DAMON_SYSFS_CMD_CLEAR_SCHEMES_TRIED_REGIONS:
+		err = damon_sysfs_clear_schemes_regions(kdamond);
+		break;
 	default:
 		break;
 	}