[RFC v2] mm/damon: add synchronous validation for commit_inputs

Liew Rui Yan
2026-03-21T14:09:36Z

Problem
=======
Writing invalid parameters to sysfs followed by 'commit_inputs=Y' fails
silently (no error returned to shell), because the validation happens
aynchronously in the kdamond.

Solution
========
To fix this, I proposed adding synchronous validation in
damon_lru_sort_commit_inputs_store() and
damon_reclaim_commit_inputs_store() before setting the 'commit_inputs'
flag. This allow users to receive immediate feedback (e.g., -EINVAL) if
the parameters are invalid.

Changes
=======
1. Added damon_lru_sort_commit_inputs_store() and
damon_reclaim_commit_inputs_store() to handle parameter validation
before setting 'commit_inputs'.
2. Added damon_validate_attrs() to centralize validation logic.

This change is motivated from another discussion [1].

[1] https://lore.kernel.org/20260318153731.97470-1-aethernet65535@gmail.com

Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
---
Changes from RFC-v1:
- Remove question from commit message area.
- Added synchronous validation for DAMON_RECLAIM.
- Rename damon_valid_attrs() -> damon_validate_attrs().
- Exported a new function damon_validate_attrs() and declared it in
damon.h.
- Link to RFC-v1: https://lore.kernel.org/20260321002642.22712-1-aethernet65535@gmail.com

include/linux/damon.h | 2 ++
mm/damon/core.c | 34 +++++++++++++++++++++++++---------
mm/damon/lru_sort.c | 34 +++++++++++++++++++++++++++++++++-
mm/damon/reclaim.c | 34 +++++++++++++++++++++++++++++++++-
4 files changed, 93 insertions(+), 11 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index d9a3babbafc1..00ca58dbe978 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -997,6 +997,8 @@ int damon_set_region_biggest_system_ram_default(struct damon_target *t,
unsigned long addr_unit,
unsigned long min_region_sz);

+int damon_validate_attrs(struct damon_attrs *attrs);
+
#endif /* CONFIG_DAMON */

#endif /* _DAMON_H */
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 4dae03a37f9a..a459cdcaaed2 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -751,6 +751,27 @@ static bool damon_valid_intervals_goal(struct damon_attrs *attrs)
return true;
}

+/**
+ * damon_validate_attrs() - Check if the given DAMON attributes are valid.
+ * @attrs: attributes to be checked
+ *
+ * Return: 0 if valid, negative error code otherwise.
+ */
+int damon_validate_attrs(struct damon_attrs *attrs)
+{
+ if (!damon_valid_intervals_goal(attrs))
+ return -EINVAL;
+ if (attrs->min_nr_regions < 3)
+ return -EINVAL;
+ if (attrs->min_nr_regions > attrs->max_nr_regions)
+ return -EINVAL;
+ if (attrs->sample_interval > attrs->aggr_interval)
+ return -EINVAL;
+
+ return 0;
+}
+EXPORT_SYMBOL(damon_validate_attrs);
+
/**
* damon_set_attrs() - Set attributes for the monitoring.
* @ctx: monitoring context
@@ -778,16 +799,11 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
struct damos *s;
bool aggregating = ctx->passed_sample_intervals <
ctx->next_aggregation_sis;
+ int err;

- if (!damon_valid_intervals_goal(attrs))
- return -EINVAL;
-
- if (attrs->min_nr_regions < 3)
- return -EINVAL;
- if (attrs->min_nr_regions > attrs->max_nr_regions)
- return -EINVAL;
- if (attrs->sample_interval > attrs->aggr_interval)
- return -EINVAL;
+ err = damon_validate_attrs(attrs);
+ if (err)
+ return err;

/* calls from core-external doesn't set this. */
if (!attrs->aggr_samples)
diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
index 554559d72976..883860721d3b 100644
--- a/mm/damon/lru_sort.c
+++ b/mm/damon/lru_sort.c
@@ -39,7 +39,6 @@ static bool enabled __read_mostly;
* the re-reading, DAMON_LRU_SORT will be disabled.
*/
static bool commit_inputs __read_mostly;
-module_param(commit_inputs, bool, 0600);

/*
* Desired active to [in]active memory ratio in bp (1/10,000).
@@ -361,6 +360,39 @@ static int damon_lru_sort_handle_commit_inputs(void)
return err;
}

+static int damon_lru_sort_commit_inputs_store(const char *val,
+ const struct kernel_param *kp)
+{
+ struct damon_attrs attrs;
+ bool yes;
+ int err;
+
+ err = kstrtobool(val, &yes);
+ if (err)
+ return err;
+
+ if (commit_inputs == yes)
+ return 0;
+
+ if (!yes)
+ return 0;
+
+ attrs = damon_lru_sort_mon_attrs;
+ err = damon_validate_attrs(&attrs);
+ if (err)
+ return err;
+
+ commit_inputs = yes;
+ return err;
+}
+
+static const struct kernel_param_ops commit_inputs_param_ops = {
+ .set = damon_lru_sort_commit_inputs_store,
+ .get = param_get_bool,
+};
+
+module_param_cb(commit_inputs, &commit_inputs_param_ops, &commit_inputs, 0600);
+
static int damon_lru_sort_damon_call_fn(void *arg)
{
struct damon_ctx *c = arg;
diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index 86da14778658..6ea44b02cc76 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -39,7 +39,6 @@ static bool enabled __read_mostly;
* re-reading, DAMON_RECLAIM will be disabled.
*/
static bool commit_inputs __read_mostly;
-module_param(commit_inputs, bool, 0600);

/*
* Time threshold for cold memory regions identification in microseconds.
@@ -267,6 +266,39 @@ static int damon_reclaim_handle_commit_inputs(void)
return err;
}

+static int damon_reclaim_commit_inputs_store(const char *val,
+ const struct kernel_param *kp)
+{
+ struct damon_attrs attrs;
+ bool yes;
+ int err;
+
+ err = kstrtobool(val, &yes);
+ if (err)
+ return err;
+
+ if (commit_inputs == yes)
+ return 0;
+
+ if (!yes)
+ return 0;
+
+ attrs = damon_reclaim_mon_attrs;
+ err = damon_validate_attrs(&attrs);
+ if (err)
+ return err;
+
+ commit_inputs = yes;
+ return err;
+}
+
+static const struct kernel_param_ops commit_inputs_param_ops = {
+ .set = damon_reclaim_commit_inputs_store,
+ .get = param_get_bool,
+};
+
+module_param_cb(commit_inputs, &commit_inputs_param_ops, &commit_inputs, 0600);
+
static int damon_reclaim_damon_call_fn(void *arg)
{
struct damon_ctx *c = arg;
--
2.53.0