mm/damon/sysfs: implement DAMOS tried regions update command

Implement the code for filling the data of 'tried_regions' DAMON sysfs
directory.  With this commit, DAMON sysfs interface users can write a
special keyword, 'update_schemes_tried_regions' to the corresponding
'state' file of the kdamond.  Then, DAMON sysfs interface will collect the
tried regions information using the 'before_damos_apply()' callback for
one aggregation interval and populate scheme region directories with the
values.

[sj@kernel.org: skip tried regions update if the scheme directory was removed]
  Link: https://lkml.kernel.org/r/20221114182954.4745-2-sj@kernel.org
Link: https://lkml.kernel.org/r/20221101220328.95765-5-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

@@ -44,3 +44,9 @@ int damon_sysfs_set_schemes(struct damon_ctx *ctx,
 void damon_sysfs_schemes_update_stats(
 		struct damon_sysfs_schemes *sysfs_schemes,
 		struct damon_ctx *ctx);
+
+int damon_sysfs_schemes_update_regions_start(
+		struct damon_sysfs_schemes *sysfs_schemes,
+		struct damon_ctx *ctx);
+
+int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx);

mm/damon/sysfs-schemes.c

@@ -1244,3 +1244,83 @@ void damon_sysfs_schemes_update_stats(
 		sysfs_stats->qt_exceeds = scheme->stat.qt_exceeds;
 	}
 }
+
+/*
+ * damon_sysfs_schemes that need to update its schemes regions dir.  Protected
+ * by damon_sysfs_lock
+ */
+static struct damon_sysfs_schemes *damon_sysfs_schemes_for_damos_callback;
+static int damon_sysfs_schemes_region_idx;
+
+/*
+ * DAMON callback that called before damos apply.  While this callback is
+ * registered, damon_sysfs_lock should be held to ensure the regions
+ * directories exist.
+ */
+static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
+		struct damon_target *t, struct damon_region *r,
+		struct damos *s)
+{
+	struct damos *scheme;
+	struct damon_sysfs_scheme_regions *sysfs_regions;
+	struct damon_sysfs_scheme_region *region;
+	struct damon_sysfs_schemes *sysfs_schemes =
+		damon_sysfs_schemes_for_damos_callback;
+	int schemes_idx = 0;
+
+	damon_for_each_scheme(scheme, ctx) {
+		if (scheme == s)
+			break;
+		schemes_idx++;
+	}
+
+	/* user could have removed the scheme sysfs dir */
+	if (schemes_idx >= sysfs_schemes->nr)
+		return 0;
+
+	sysfs_regions = sysfs_schemes->schemes_arr[schemes_idx]->tried_regions;
+	region = damon_sysfs_scheme_region_alloc(r);
+	list_add_tail(&region->list, &sysfs_regions->regions_list);
+	sysfs_regions->nr_regions++;
+	if (kobject_init_and_add(&region->kobj,
+				&damon_sysfs_scheme_region_ktype,
+				&sysfs_regions->kobj, "%d",
+				damon_sysfs_schemes_region_idx++)) {
+		kobject_put(&region->kobj);
+	}
+	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)
+{
+	struct damos *scheme;
+	int schemes_idx = 0;
+
+	damon_for_each_scheme(scheme, ctx) {
+		struct damon_sysfs_scheme *sysfs_scheme;
+
+		sysfs_scheme = sysfs_schemes->schemes_arr[schemes_idx++];
+		damon_sysfs_scheme_regions_rm_dirs(
+				sysfs_scheme->tried_regions);
+	}
+
+	damon_sysfs_schemes_for_damos_callback = sysfs_schemes;
+	ctx->callback.before_damos_apply = damon_sysfs_before_damos_apply;
+	return 0;
+}
+
+/*
+ * Called from damon_sysfs_cmd_request_callback under damon_sysfs_lock.  Caller
+ * should unlock damon_sysfs_lock which held before
+ * damon_sysfs_schemes_update_regions_start()
+ */
+int damon_sysfs_schemes_update_regions_stop(struct damon_ctx *ctx)
+{
+	damon_sysfs_schemes_for_damos_callback = NULL;
+	ctx->callback.before_damos_apply = NULL;
+	damon_sysfs_schemes_region_idx = 0;
+	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_REGIONS: Update schemes tried
+	 * regions
+	 */
+	DAMON_SYSFS_CMD_UPDATE_SCHEMES_TRIED_REGIONS,
 	/*
 	 * @NR_DAMON_SYSFS_CMDS: Total number of DAMON sysfs commands.
 	 */
@@ -1011,6 +1016,7 @@ static const char * const damon_sysfs_cmd_strs[] = {
 	"off",
 	"commit",
 	"update_schemes_stats",
+	"update_schemes_tried_regions",
 };
 
 /*
@@ -1193,6 +1199,16 @@ static int damon_sysfs_set_targets(struct damon_ctx *ctx,
 static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
 {
 	struct damon_target *t, *next;
+	struct damon_sysfs_kdamond *kdamond;
+
+	/* 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) {
+		damon_sysfs_schemes_update_regions_stop(ctx);
+		mutex_unlock(&damon_sysfs_lock);
+	}
 
 	if (!damon_target_has_pid(ctx))
 		return;
@@ -1225,6 +1241,27 @@ static int damon_sysfs_upd_schemes_stats(struct damon_sysfs_kdamond *kdamond)
 	return 0;
 }
 
+static int damon_sysfs_upd_schemes_regions_start(
+		struct damon_sysfs_kdamond *kdamond)
+{
+	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);
+}
+
+static int damon_sysfs_upd_schemes_regions_stop(
+		struct damon_sysfs_kdamond *kdamond)
+{
+	struct damon_ctx *ctx = kdamond->damon_ctx;
+
+	if (!ctx)
+		return -EINVAL;
+	return damon_sysfs_schemes_update_regions_stop(ctx);
+}
+
 static inline bool damon_sysfs_kdamond_running(
 		struct damon_sysfs_kdamond *kdamond)
 {
@@ -1277,10 +1314,12 @@ static int damon_sysfs_commit_input(struct damon_sysfs_kdamond *kdamond)
 static int damon_sysfs_cmd_request_callback(struct damon_ctx *c)
 {
 	struct damon_sysfs_kdamond *kdamond;
+	static bool damon_sysfs_schemes_regions_updating;
 	int err = 0;
 
 	/* avoid deadlock due to concurrent state_store('off') */
-	if (!mutex_trylock(&damon_sysfs_lock))
+	if (!damon_sysfs_schemes_regions_updating &&
+			!mutex_trylock(&damon_sysfs_lock))
 		return 0;
 	kdamond = damon_sysfs_cmd_request.kdamond;
 	if (!kdamond || kdamond->damon_ctx != c)
@@ -1292,13 +1331,27 @@ 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_REGIONS:
+		if (!damon_sysfs_schemes_regions_updating) {
+			err = damon_sysfs_upd_schemes_regions_start(kdamond);
+			if (!err) {
+				damon_sysfs_schemes_regions_updating = true;
+				goto keep_lock_out;
+			}
+		} else {
+			err = damon_sysfs_upd_schemes_regions_stop(kdamond);
+			damon_sysfs_schemes_regions_updating = false;
+		}
+		break;
 	default:
 		break;
 	}
 	/* Mark the request as invalid now. */
 	damon_sysfs_cmd_request.kdamond = NULL;
 out:
-	mutex_unlock(&damon_sysfs_lock);
+	if (!damon_sysfs_schemes_regions_updating)
+		mutex_unlock(&damon_sysfs_lock);
+keep_lock_out:
 	return err;
 }