[PATCH v13 064/137] flex_proportions: Allow N events instead of 1

Matthew Wilcox (Oracle)
2021-07-12T03:42:20Z

When batching events (such as writing back N pages in a single I/O), it
is better to do one flex_proportion operation instead of N. There is
only one caller of __fprop_inc_percpu_max(), and it's the one we're
going to change in the next patch, so rename it instead of adding a
compatibility wrapper.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
include/linux/flex_proportions.h | 9 +++++----
lib/flex_proportions.c | 28 +++++++++++++++++++---------
mm/page-writeback.c | 4 ++--
3 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/include/linux/flex_proportions.h b/include/linux/flex_proportions.h
index c12df59d3f5f..3e378b1fb0bc 100644
--- a/include/linux/flex_proportions.h
+++ b/include/linux/flex_proportions.h
@@ -83,9 +83,10 @@ struct fprop_local_percpu {

int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp);
void fprop_local_destroy_percpu(struct fprop_local_percpu *pl);
-void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl);
-void __fprop_inc_percpu_max(struct fprop_global *p, struct fprop_local_percpu *pl,
- int max_frac);
+void __fprop_add_percpu(struct fprop_global *p, struct fprop_local_percpu *pl,
+ long nr);
+void __fprop_add_percpu_max(struct fprop_global *p,
+ struct fprop_local_percpu *pl, int max_frac, long nr);
void fprop_fraction_percpu(struct fprop_global *p,
struct fprop_local_percpu *pl, unsigned long *numerator,
unsigned long *denominator);
@@ -96,7 +97,7 @@ void fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
unsigned long flags;

local_irq_save(flags);
- __fprop_inc_percpu(p, pl);
+ __fprop_add_percpu(p, pl, 1);
local_irq_restore(flags);
}

diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c
index 451543937524..53e7eb1dd76c 100644
--- a/lib/flex_proportions.c
+++ b/lib/flex_proportions.c
@@ -217,11 +217,12 @@ static void fprop_reflect_period_percpu(struct fprop_global *p,
}

/* Event of type pl happened */
-void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
+void __fprop_add_percpu(struct fprop_global *p, struct fprop_local_percpu *pl,
+ long nr)
{
fprop_reflect_period_percpu(p, pl);
- percpu_counter_add_batch(&pl->events, 1, PROP_BATCH);
- percpu_counter_add(&p->events, 1);
+ percpu_counter_add_batch(&pl->events, nr, PROP_BATCH);
+ percpu_counter_add(&p->events, nr);
}

void fprop_fraction_percpu(struct fprop_global *p,
@@ -253,20 +254,29 @@ void fprop_fraction_percpu(struct fprop_global *p,
}

/*
- * Like __fprop_inc_percpu() except that event is counted only if the given
+ * Like __fprop_add_percpu() except that event is counted only if the given
* type has fraction smaller than @max_frac/FPROP_FRAC_BASE
*/
-void __fprop_inc_percpu_max(struct fprop_global *p,
- struct fprop_local_percpu *pl, int max_frac)
+void __fprop_add_percpu_max(struct fprop_global *p,
+ struct fprop_local_percpu *pl, int max_frac, long nr)
{
if (unlikely(max_frac < FPROP_FRAC_BASE)) {
unsigned long numerator, denominator;
+ s64 tmp;

fprop_fraction_percpu(p, pl, &numerator, &denominator);
- if (numerator >
- (((u64)denominator) * max_frac) >> FPROP_FRAC_SHIFT)
+ /* Adding 'nr' to fraction exceeds max_frac/FPROP_FRAC_BASE? */
+ tmp = (u64)denominator * max_frac -
+ ((u64)numerator << FPROP_FRAC_SHIFT);
+ if (tmp < 0) {
+ /* Maximum fraction already exceeded? */
return;
+ } else if (tmp < nr * (FPROP_FRAC_BASE - max_frac)) {
+ /* Add just enough for the fraction to saturate */
+ nr = div_u64(tmp + FPROP_FRAC_BASE - max_frac - 1,
+ FPROP_FRAC_BASE - max_frac);
+ }
}

- __fprop_inc_percpu(p, pl);
+ __fprop_add_percpu(p, pl, nr);
}
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index e677e79c7b9b..63c0dd9f8bf7 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -566,8 +566,8 @@ static void wb_domain_writeout_inc(struct wb_domain *dom,
struct fprop_local_percpu *completions,
unsigned int max_prop_frac)
{
- __fprop_inc_percpu_max(&dom->completions, completions,
- max_prop_frac);
+ __fprop_add_percpu_max(&dom->completions, completions,
+ max_prop_frac, 1);
/* First event after period switching was turned off? */
if (unlikely(!dom->period_time)) {
/*
--
2.30.2