[RFC PATCH 1/5] mm/damon/core: add damon_target->obsolete for pin-point removal

SeongJae Park
2025-10-16T21:47:42Z

DAMON's monitoring targets parameters update function,
damon_commit_targets(), is not providing a way to remove a target in the
middle of existing targets list. Extend the API by adding a field to
struct damon_target. If the field of a damon_commit_targets() source
target is set, it indicates the matcing target on the existing targets
list is obsolete. damon_commit_targets() understands that and remove
those from the list, while respecting the index based matching for other
non-obsolete targets.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
include/linux/damon.h | 6 ++++++
mm/damon/core.c | 10 +++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 524dea87cac7..8a7b45b9e40d 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -92,17 +92,23 @@ struct damon_region {
* @nr_regions: Number of monitoring target regions of this target.
* @regions_list: Head of the monitoring target regions of this target.
* @list: List head for siblings.
+ * @obsolete: Whether the commit destination target is obsolete.
*
* Each monitoring context could have multiple targets. For example, a context
* for virtual memory address spaces could have multiple target processes. The
* @pid should be set for appropriate &struct damon_operations including the
* virtual address spaces monitoring operations.
+ *
+ * @obsolte is used only for damon_commit_targets() source targets, to specify
+ * the matching destination targets are obsolte. Read damon_commit_targets()
+ * to see how it is handled.
*/
struct damon_target {
struct pid *pid;
unsigned int nr_regions;
struct list_head regions_list;
struct list_head list;
+ bool obsolete;
};

/**
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 70e66562a1b3..3242a9573db0 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -492,6 +492,7 @@ struct damon_target *damon_new_target(void)
t->nr_regions = 0;
INIT_LIST_HEAD(&t->regions_list);
INIT_LIST_HEAD(&t->list);
+ t->obsolete = false;

return t;
}
@@ -1213,7 +1214,11 @@ static int damon_commit_targets(

damon_for_each_target_safe(dst_target, next, dst) {
src_target = damon_nth_target(i++, src);
- if (src_target) {
+ /*
+ * If src target is obsolete, do not commit the parameters to
+ * the dst target, and further remove the dst target.
+ */
+ if (src_target && !src_target->obsolete) {
err = damon_commit_target(
dst_target, damon_target_has_pid(dst),
src_target, damon_target_has_pid(src),
@@ -1236,6 +1241,9 @@ static int damon_commit_targets(
damon_for_each_target_safe(src_target, next, src) {
if (j++ < i)
continue;
+ /* target to remove has no matching dst */
+ if (src_target->obsolete)
+ return -EINVAL;
new_target = damon_new_target();
if (!new_target)
return -ENOMEM;
--
2.47.3