diff options
| author | SJ Park <sj@kernel.org> | 2026-07-12 09:54:30 -0700 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-08-06 18:56:57 -0700 |
| commit | 0250dbe08c730d003ef9f484da56ae09a1ea0c4c (patch) | |
| tree | 3591765a12bf0d52fa1ff38839079c0250b7d9e7 | |
| parent | 824d80962cf277f1c02e781bb18684b588111612 (diff) | |
mm/damon/core: skip aging from repeated aggressive merging
The number of DAMON regions could temporarily exceed the user-defined
maximum number of regions limit for corner cases. For example, users
could lower the limit via runtime parameters update. For such a case,
kdamond_merge_regions() repeats merging regions in the case doubling the
merge threshold. The repeated merge operation could update the age of
regions multiple times. This corrupts the monitoring results. Fix the
issue by asking the merge operation to skip aging for the corner case.
The user impact is degradation of the monitoring quality. The impact
should be mild, since the degradation is only temporal, and it is not
common to happen in realistic setups.
The issue was discovered [1,2] by Sashiko.
Link: https://lore.kernel.org/20260712165432.87609-1-sj@kernel.org
Link: https://lore.kernel.org/20260621203548.10718-1-sj@kernel.org [1]
Link: https://lore.kernel.org/20260709145425.96247-1-sj@kernel.org [2]
Fixes: 310d6c15e910 ("mm/damon/core: merge regions aggressively when max_nr_regions is unmet")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.10
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | mm/damon/core.c | 21 | ||||
| -rw-r--r-- | mm/damon/tests/core-kunit.h | 2 |
2 files changed, 14 insertions, 9 deletions
diff --git a/mm/damon/core.c b/mm/damon/core.c index 806a67d02a6e..6c4215cc809e 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -3308,7 +3308,7 @@ static unsigned int damon_merge_score(struct damon_region *r, bool last, * sz_limit size upper limit of each region */ static void damon_merge_regions_of(struct damon_target *t, unsigned int thres, - unsigned long sz_limit, struct damon_ctx *ctx) + unsigned long sz_limit, struct damon_ctx *ctx, bool count_age) { struct damon_region *r, *prev = NULL, *next; bool use_probe_hits = damon_has_probe_weights(ctx); @@ -3319,12 +3319,14 @@ static void damon_merge_regions_of(struct damon_target *t, unsigned int thres, score = damon_merge_score(r, false, ctx, use_probe_hits); last_score = damon_merge_score(r, true, ctx, use_probe_hits); - if (abs_diff(score, last_score) > thres) - r->age = 0; - else if ((score == 0) != (last_score == 0)) - r->age = 0; - else - r->age++; + if (count_age) { + if (abs_diff(score, last_score) > thres) + r->age = 0; + else if ((score == 0) != (last_score == 0)) + r->age = 0; + else + r->age++; + } if (!prev) goto set_prev_continue; @@ -3366,15 +3368,18 @@ static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold, struct damon_target *t; unsigned int nr_regions; unsigned int max_thres; + bool count_age = true; max_thres = c->attrs.aggr_interval / (c->attrs.sample_interval ? c->attrs.sample_interval : 1); do { nr_regions = 0; damon_for_each_target(t, c) { - damon_merge_regions_of(t, threshold, sz_limit, c); + damon_merge_regions_of(t, threshold, sz_limit, c, + count_age); nr_regions += damon_nr_regions(t); } + count_age = false; threshold = max(1, threshold * 2); } while (nr_regions > c->attrs.max_nr_regions && threshold / 2 < max_thres); diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h index 73cb8fcdf07e..485472ddebd1 100644 --- a/mm/damon/tests/core-kunit.h +++ b/mm/damon/tests/core-kunit.h @@ -257,7 +257,7 @@ static void damon_test_merge_regions_of(struct kunit *test) damon_add_region(r, t); } - damon_merge_regions_of(t, 9, 9999, ctx); + damon_merge_regions_of(t, 9, 9999, ctx, true); /* 0-112, 114-130, 130-156, 156-170, 170-230, 230-10170 */ KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 6u); for (i = 0; i < 6; i++) { |