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mm/damon/core: always update ->last_nr_accesses for intervals change

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Each iteration of kdamond_fn() main loop caches and use the next
aggregation time (next_aggregation_sis) because it can be updated in the
middle, inside kdamond_call().  If that happens,
damon_update_monitoring_result() is called for scaling the access
frequency information of each region according to the changed intervals. 
The function does not update damon_region->last_nr_accesses when it is at
the end of the aggregation, because it will anyway be reset after the
function is executed, in kdamond_reset_aggregated().

Let's suppose damon_nr_accesses_mvsum() is called with the not yet updated
last_nr_accesses.  It will use the fresh next_aggregation_sis in the
context instead of the cached one, unlike kdamond_fn().  As a result, use
of not updated last_nr_acceses with the updated next_aggregation_sis
result in returning wrong value.

There is no such damon_nr_accesses_nvsum() call at the moment, so this is
no problem.  It is planned to add such calls, though.  Prevent the issue
by updating last_nr_accesses always.  This adds overhead, but that's fine
because the overhead is not big, and it is anyway not a fast path.

Link: https://lore.kernel.org/20260630040812.149729-4-sj@kernel.org
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
SJ Park
2026-06-29 21:07:56 -07:00
committed by Andrew Morton
parent f8dbb118fa
commit a44821c65c
1 changed files with 2 additions and 2 deletions
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4
mm/damon/core.c
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@@ -884,6 +884,8 @@ static void damon_update_monitoring_result(struct damon_region *r,
struct damon_attrs *old_attrs, struct damon_attrs *new_attrs,
bool aggregating)
{
r->last_nr_accesses = damon_nr_accesses_for_new_attrs(
r->last_nr_accesses, old_attrs, new_attrs);
if (!aggregating) {
r->nr_accesses = damon_nr_accesses_for_new_attrs(
r->nr_accesses, old_attrs, new_attrs);
@@ -895,8 +897,6 @@ static void damon_update_monitoring_result(struct damon_region *r,
* interval. In other words, make the status like
* kdamond_reset_aggregated() is called.
*/
r->last_nr_accesses = damon_nr_accesses_for_new_attrs(
r->last_nr_accesses, old_attrs, new_attrs);
r->nr_accesses_bp = r->last_nr_accesses * 10000;
r->nr_accesses = 0;
}