mm/damon/stat: expose the current tuned aggregation interval

Patch series "mm/damon/stat: expose auto-tuned intervals and non-idle
ages".

DAMON_STAT is intentionally providing limited information for easy
consumption of the information.  From production fleet level usages, below
limitations are found, though.

The aggregation interval of DAMON_STAT represents the granularity of the
memory_idle_ms_percentiles.  But the interval is auto-tuned and not
exposed to users, so users cannot know the granularity.

All memory regions of non-zero (positive) nr_accesses are treated as
having zero idle time.  A significant portion of production systems have
such zero idle time.  Hence breakdown of warm and hot data is nearly
impossible.

Make following changes to overcome the limitations.  Expose the auto-tuned
aggregation interval with a new parameter named aggr_interval_us.  Expose
the age of non-zero nr_accesses (how long >0 access frequency the region
retained) regions as a negative idle time.

This patch (of 2):

DAMON_STAT calculates the idle time for a region as the region's age
multiplied by the aggregation interval.  That is, the aggregation interval
is the granularity of the idle time.  Since the aggregation interval is
auto-tuned and not exposed to users, however, users cannot easily know in
what granularity the stat is made.  Expose the tuned aggregation interval
in microseconds via a new parameter, aggr_interval_us.

Link: https://lkml.kernel.org/r/20250916183127.65708-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20250916183127.65708-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/stat.c b/mm/damon/stat.c
index c4fbd8cfa5eb62da0ed3a474c4fef184a2099842..1a8465abef4ab857fdcd0c27907438cf8b08e3d7 100644 (file)
--- a/mm/damon/stat.c
+++ b/mm/damon/stat.c
@@ -39,6 +39,11 @@ module_param_array(memory_idle_ms_percentiles, ulong, NULL, 0400);
 MODULE_PARM_DESC(memory_idle_ms_percentiles,
                "Memory idle time percentiles in milliseconds");
 
+static unsigned long aggr_interval_us;
+module_param(aggr_interval_us, ulong, 0400);
+MODULE_PARM_DESC(aggr_interval_us,
+               "Current tuned aggregation interval in microseconds");
+
 static struct damon_ctx *damon_stat_context;
 
 static void damon_stat_set_estimated_memory_bandwidth(struct damon_ctx *c)
@@ -133,6 +138,7 @@ static int damon_stat_damon_call_fn(void *data)
                return 0;
        last_refresh_jiffies = jiffies;
 
+       aggr_interval_us = c->attrs.aggr_interval;
        damon_stat_set_estimated_memory_bandwidth(c);
        damon_stat_set_idletime_percentiles(c);
        return 0;