mm/damon/sysfs-schemes: implement max_nr_snapshots file

Add a new DAMON sysfs file for setting and getting the newly introduced
per-DAMON-snapshot level DAMOS deactivation control parameter,
max_nr_snapshots.  The file has a name same to the parameter and placed
under the damos stat directory.

Link: https://lkml.kernel.org/r/20251216080128.42991-9-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index b7fcd7590ab38c143377f8ab4d853eb413d66191..19bc2288cd68cd28e13701d3a780624d0388c779 100644 (file)
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -205,6 +205,7 @@ struct damon_sysfs_stats {
        unsigned long sz_ops_filter_passed;
        unsigned long qt_exceeds;
        unsigned long nr_snapshots;
+       unsigned long max_nr_snapshots;
 };
 
 static struct damon_sysfs_stats *damon_sysfs_stats_alloc(void)
@@ -275,6 +276,28 @@ static ssize_t nr_snapshots_show(struct kobject *kobj,
        return sysfs_emit(buf, "%lu\n", stats->nr_snapshots);
 }
 
+static ssize_t max_nr_snapshots_show(struct kobject *kobj,
+               struct kobj_attribute *attr, char *buf)
+{
+       struct damon_sysfs_stats *stats = container_of(kobj,
+                       struct damon_sysfs_stats, kobj);
+
+       return sysfs_emit(buf, "%lu\n", stats->max_nr_snapshots);
+}
+
+static ssize_t max_nr_snapshots_store(struct kobject *kobj,
+               struct kobj_attribute *attr, const char *buf, size_t count)
+{
+       struct damon_sysfs_stats *stats = container_of(kobj,
+                       struct damon_sysfs_stats, kobj);
+       unsigned long max_nr_snapshots, err = kstrtoul(buf, 0, &max_nr_snapshots);
+
+       if (err)
+               return err;
+       stats->max_nr_snapshots = max_nr_snapshots;
+       return count;
+}
+
 static void damon_sysfs_stats_release(struct kobject *kobj)
 {
        kfree(container_of(kobj, struct damon_sysfs_stats, kobj));
@@ -301,6 +324,9 @@ static struct kobj_attribute damon_sysfs_stats_qt_exceeds_attr =
 static struct kobj_attribute damon_sysfs_stats_nr_snapshots_attr =
                __ATTR_RO_MODE(nr_snapshots, 0400);
 
+static struct kobj_attribute damon_sysfs_stats_max_nr_snapshots_attr =
+               __ATTR_RW_MODE(max_nr_snapshots, 0600);
+
 static struct attribute *damon_sysfs_stats_attrs[] = {
        &damon_sysfs_stats_nr_tried_attr.attr,
        &damon_sysfs_stats_sz_tried_attr.attr,
@@ -309,6 +335,7 @@ static struct attribute *damon_sysfs_stats_attrs[] = {
        &damon_sysfs_stats_sz_ops_filter_passed_attr.attr,
        &damon_sysfs_stats_qt_exceeds_attr.attr,
        &damon_sysfs_stats_nr_snapshots_attr.attr,
+       &damon_sysfs_stats_max_nr_snapshots_attr.attr,
        NULL,
 };
 ATTRIBUTE_GROUPS(damon_sysfs_stats);
@@ -2732,6 +2759,7 @@ static struct damos *damon_sysfs_mk_scheme(
                damon_destroy_scheme(scheme);
                return NULL;
        }
+       scheme->max_nr_snapshots = sysfs_scheme->stats->max_nr_snapshots;
        return scheme;
 }