[PATCH] mm/damon: Fix paddr target id problem

[SeongJae Park]

The target id for 'paddr' is meaningless, but we set it as '-1' for fun
and smooth interaction with the user space interfaces.  However, the
target ids are 'unsigned long' and thus using '-1' makes no sense.  This
commit changes the fake number to another funny but unsigned number,
'42'.

Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
---
 Documentation/admin-guide/mm/damon/usage.rst | 4 ++--
 mm/damon.c                                   | 2 +-
 tools/damon/_damon.py                        | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index 88b8e9254a7e..3e2f1519c96a 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -334,12 +334,12 @@ check it again::
 Users can also monitor the physical memory address space of the system by
 writing a special keyword, "``paddr\n``" to the file.  Because physical address
 space monitoring doesn't support multiple targets, reading the file will show a
-fake value, ``-1``, as below::
+fake value, ``42``, as below::

     # cd <debugfs>/damon
     # echo paddr > target_ids
     # cat target_ids
-    -1
+    42

 Note that setting the target ids doesn't start the monitoring.

diff --git a/mm/damon.c b/mm/damon.c
index a9757a0e5cf7..66268cb45b51 100644
--- a/mm/damon.c
+++ b/mm/damon.c
@@ -2047,7 +2047,7 @@ static ssize_t debugfs_target_ids_write(struct file *file,
                ctx->target_valid = NULL;

                /* target id is meaningless here, but we set it just for fun */
-               snprintf(kbuf, count, "-1    ");
+               snprintf(kbuf, count, "42    ");
        } else {
                /* Configure the context for virtual memory monitoring */
                ctx->init_target_regions = kdamond_init_vm_regions;
diff --git a/tools/damon/_damon.py b/tools/damon/_damon.py
index cf14a0d59b94..6ff278117e84 100644
--- a/tools/damon/_damon.py
+++ b/tools/damon/_damon.py
@@ -28,7 +28,7 @@ def set_target(tid, init_regions=[]):
         return 0

     if tid == 'paddr':
-        tid = -1
+        tid = 42
     string = ' '.join(['%s %d %d' % (tid, r[0], r[1]) for r in init_regions])
     return subprocess.call('echo "%s" > %s' % (string, debugfs_init_regions),
             shell=True, executable='/bin/bash')
--
2.17.1