mm/damon/dbgfs/init_regions: use target index instead of target id

Patch series "Remove the type-unclear target id concept".

DAMON asks each monitoring target ('struct damon_target') to have one
'unsigned long' integer called 'id', which should be unique among the
targets of same monitoring context.  Meaning of it is, however, totally up
to the monitoring primitives that registered to the monitoring context.
For example, the virtual address spaces monitoring primitives treats the
id as a 'struct pid' pointer.

This makes the code flexible but ugly, not well-documented, and
type-unsafe[1].  Also, identification of each target can be done via its
index.  For the reason, this patchset removes the concept and uses clear
type definition.

[1] https://lore.kernel.org/linux-mm/20211013154535.4aaeaaf9d0182922e405dd1e@linux-foundation.org/

This patch (of 4):

Target id is a 'unsigned long' data, which can be interpreted differently
by each monitoring primitives.  For example, it means 'struct pid *' for
the virtual address spaces monitoring, while it means nothing but an
integer to be displayed to debugfs interface users for the physical
address space monitoring.  It's flexible but makes code ugly and
type-unsafe[1].

To be prepared for eventual removal of the concept, this commit removes a
use case of the concept in 'init_regions' debugfs file handling.  In
detail, this commit replaces use of the id with the index of each target
in the context's targets list.

[1] https://lore.kernel.org/linux-mm/20211013154535.4aaeaaf9d0182922e405dd1e@linux-foundation.org/

Link: https://lkml.kernel.org/r/20211230100723.2238-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20211230100723.2238-2-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/damon/dbgfs-test.h

@@ -113,19 +113,19 @@ static void damon_dbgfs_test_set_init_regions(struct kunit *test)
 {
 	struct damon_ctx *ctx = damon_new_ctx();
 	unsigned long ids[] = {1, 2, 3};
-	/* Each line represents one region in ``<target id> <start> <end>`` */
-	char * const valid_inputs[] = {"2 10 20\n 2   20 30\n2 35 45",
-		"2 10 20\n",
-		"2 10 20\n1 39 59\n1 70 134\n  2  20 25\n",
+	/* Each line represents one region in ``<target idx> <start> <end>`` */
+	char * const valid_inputs[] = {"1 10 20\n 1   20 30\n1 35 45",
+		"1 10 20\n",
+		"1 10 20\n0 39 59\n0 70 134\n  1  20 25\n",
 		""};
 	/* Reading the file again will show sorted, clean output */
-	char * const valid_expects[] = {"2 10 20\n2 20 30\n2 35 45\n",
-		"2 10 20\n",
-		"1 39 59\n1 70 134\n2 10 20\n2 20 25\n",
+	char * const valid_expects[] = {"1 10 20\n1 20 30\n1 35 45\n",
+		"1 10 20\n",
+		"0 39 59\n0 70 134\n1 10 20\n1 20 25\n",
 		""};
-	char * const invalid_inputs[] = {"4 10 20\n",	/* target not exists */
-		"2 10 20\n 2 14 26\n",		/* regions overlap */
-		"1 10 20\n2 30 40\n 1 5 8"};	/* not sorted by address */
+	char * const invalid_inputs[] = {"3 10 20\n",	/* target not exists */
+		"1 10 20\n 1 14 26\n",		/* regions overlap */
+		"0 10 20\n1 30 40\n 0 5 8"};	/* not sorted by address */
 	char *input, *expect;
 	int i, rc;
 	char buf[256];

mm/damon/dbgfs.c

@@ -440,18 +440,20 @@ static ssize_t sprint_init_regions(struct damon_ctx *c, char *buf, ssize_t len)
 {
 	struct damon_target *t;
 	struct damon_region *r;
+	int target_idx = 0;
 	int written = 0;
 	int rc;
 
 	damon_for_each_target(t, c) {
 		damon_for_each_region(r, t) {
 			rc = scnprintf(&buf[written], len - written,
-					"%lu %lu %lu\n",
-					t->id, r->ar.start, r->ar.end);
+					"%d %lu %lu\n",
+					target_idx, r->ar.start, r->ar.end);
 			if (!rc)
 				return -ENOMEM;
 			written += rc;
 		}
+		target_idx++;
 	}
 	return written;
 }
@@ -485,22 +487,19 @@ static ssize_t dbgfs_init_regions_read(struct file *file, char __user *buf,
 	return len;
 }
 
-static int add_init_region(struct damon_ctx *c,
-			 unsigned long target_id, struct damon_addr_range *ar)
+static int add_init_region(struct damon_ctx *c, int target_idx,
+		struct damon_addr_range *ar)
 {
 	struct damon_target *t;
 	struct damon_region *r, *prev;
-	unsigned long id;
+	unsigned long idx = 0;
 	int rc = -EINVAL;
 
 	if (ar->start >= ar->end)
 		return -EINVAL;
 
 	damon_for_each_target(t, c) {
-		id = t->id;
-		if (targetid_is_pid(c))
-			id = (unsigned long)pid_vnr((struct pid *)id);
-		if (id == target_id) {
+		if (idx++ == target_idx) {
 			r = damon_new_region(ar->start, ar->end);
 			if (!r)
 				return -ENOMEM;
@@ -523,7 +522,7 @@ static int set_init_regions(struct damon_ctx *c, const char *str, ssize_t len)
 	struct damon_target *t;
 	struct damon_region *r, *next;
 	int pos = 0, parsed, ret;
-	unsigned long target_id;
+	int target_idx;
 	struct damon_addr_range ar;
 	int err;
 
@@ -533,11 +532,11 @@ static int set_init_regions(struct damon_ctx *c, const char *str, ssize_t len)
 	}
 
 	while (pos < len) {
-		ret = sscanf(&str[pos], "%lu %lu %lu%n",
-				&target_id, &ar.start, &ar.end, &parsed);
+		ret = sscanf(&str[pos], "%d %lu %lu%n",
+				&target_idx, &ar.start, &ar.end, &parsed);
 		if (ret != 3)
 			break;
-		err = add_init_region(c, target_id, &ar);
+		err = add_init_region(c, target_idx, &ar);
 		if (err)
 			goto fail;
 		pos += parsed;