mm/damon/ops-common: optimize damon_hot_score() using ilog2()

Patch series "mm/damon: repost non-hotfix reviewed patches in damon/next
tree", v2.

The first patch from Liew Rui Yan add a minor performance optimization
using ilog2() instead of inefficient manual implementation of the
functionality.

The second patch from Cheng-Han Wu fixes a minor typo:
s/parametrs/parameters/.

The third patch from Liew Rui Yan make commit_inputs operation of
DAMON_RECLAIM and DAMON_LRU_SORT synchronous to improve the user
experience.

The fourth patch from Asier Gutierrez adds a new DAMOS action,
DAMOS_COLLAPSE for deterministic DAMOS-based access-aware THP system.

This patch (of 4):

The current implementation of damon_hot_score() uses a manual for-loop to
calculate the value of 'age_in_log'.  This can be efficiently replaced by
ilog2(), which is semantically more appropriate for calculating the
logarithmic value of age.

In a simulated-kernel-module performance test with 10,000,000 iterations,
this optimization showed a significant reduction in latency (average
latency reduced from ~12ns to ~1ns).

Test results from the simulated-kernel-module:
- ilog2:
    DAMON Perf Test: Starting 10000000 iterations
    =============================================
     Total Iterations : 10000000
     Average Latency  : 1 ns
     P95 Latency      : 41 ns
     P99 Latency      : 41 ns
    ---------------------------------------------
     Range (ns)      | Count        | Percent
    ---------------------------------------------
     0-19            | 0            |      0%
     20-39           | 2625000      |     26%
     40-59           | 7374000      |     73%
     60-79           | 0            |      0%
     80-99           | 0            |      0%
     100+            | 1000         |      0%
    =============================================

- for-loop:
    DAMON Perf Test: Starting 10000000 iterations
    =============================================
     Total Iterations : 10000000
     Average Latency  : 12 ns
     P95 Latency      : 51 ns
     P99 Latency      : 60 ns
    ---------------------------------------------
     Range (ns)      | Count        | Percent
    ---------------------------------------------
     0-19            | 0            |      0%
     20-39           | 0            |      0%
     40-59           | 9862000      |     98%
     60-79           | 135000       |      1%
     80-99           | 1000         |      0%
     100+            | 2000         |      0%
    =============================================

Full raw benchmark results can be found at [1].

Link: https://lore.kernel.org/20260426231619.107231-1-sj@kernel.org
Link: https://lore.kernel.org/20260426231619.107231-2-sj@kernel.org
Link: https://github.com/aethernet65535/damon-hot-score-fls-optimize/tree/master/result-raw
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
Cc: Cheng-Han Wu <hank20010209@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index 8c6d613425c1314d4d1825ad7661388290d669d3..3a0ddc3ac71966d84d1c26bc7355ef10c1cd2f38 100644 (file)
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -117,9 +117,12 @@ int damon_hot_score(struct damon_ctx *c, struct damon_region *r,
                damon_max_nr_accesses(&c->attrs);
 
        age_in_sec = (unsigned long)r->age * c->attrs.aggr_interval / 1000000;
-       for (age_in_log = 0; age_in_log < DAMON_MAX_AGE_IN_LOG && age_in_sec;
-                       age_in_log++, age_in_sec >>= 1)
-               ;
+       if (age_in_sec)
+               age_in_log = min_t(int, ilog2(age_in_sec) + 1,
+                               DAMON_MAX_AGE_IN_LOG);
+       else
+               age_in_log = 0;
+
 
        /* If frequency is 0, higher age means it's colder */
        if (freq_subscore == 0)