[PATCH 2/2] mm/damon/core: eliminate hot-path integer division in damon_max_nr_accesses()

[Josh Law <objecting@objecting.org>]

Hardware integer division is slow. The function damon_max_nr_accesses(),
which is called very frequently (e.g., once per region per sample
interval inside damon_update_region_access_rate), performs an integer
division: attrs->aggr_interval / attrs->sample_interval.

However, the struct damon_attrs already caches this exact ratio in the
internal field aggr_samples (since earlier commits). We can eliminate
the hardware division in the hot path by simply returning aggr_samples.

This significantly reduces the CPU cycle overhead of updating the access
rates for thousands of regions.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 include/linux/damon.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 6bd71546f7b2..fffdb08326a2 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -960,8 +960,7 @@ static inline bool damon_target_has_pid(const struct damon_ctx *ctx)
 static inline unsigned int damon_max_nr_accesses(const struct damon_attrs *attrs)
 {
 	/* {aggr,sample}_interval are unsigned long, hence could overflow */
-	return min(attrs->aggr_interval / attrs->sample_interval,
-			(unsigned long)UINT_MAX);
+	return min(attrs->aggr_samples, (unsigned long)UINT_MAX);
 }
 
 
-- 
2.34.1