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

Jan Kara
2021-07-13T14:39:53Z

On Mon 12-07-21 04:05:48, Matthew Wilcox (Oracle) wrote:
> 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>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> 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
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR