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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>
This commit is contained in:
SeongJae Park 2025-09-16 11:31:26 -07:00 committed by Andrew Morton
parent d93871f473
commit cc7ceb1d14
1 changed files with 6 additions and 0 deletions
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6
mm/damon/stat.c
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@ -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;