Re: [PATCH 03/10] lib: add a batch size to fprop_global

[Jan Kara <jack@suse.cz>]

On Wed 22-11-17 09:47:16, Jan Kara wrote:
> On Tue 14-11-17 16:56:49, Josef Bacik wrote:
> > From: Josef Bacik <jbacik@fb.com>
> > 
> > The flexible proportion stuff has been used to track how many pages we
> > are writing out over a period of time, so counts everything in single
> > increments.  If we wanted to use another base value we need to be able
> > to adjust the batch size to fit our the units we'll be using for the
> > proportions.
> > 
> > Signed-off-by: Josef Bacik <jbacik@fb.com>
> 
> Frankly, I had to look into the code to understand what the patch is about.
> Can we rephrase the changelog like:
> 
> Currently flexible proportion code is using fixed per-cpu counter batch size
> since all the counters use only increment / decrement to track number of
> pages which completed writeback. When we start tracking amount of done
> writeback in different units, we need to update per-cpu counter batch size
> accordingly. Make counter batch size configurable on a per-proportion
> domain basis to allow for this.

Actually, now that I'm looking at other patches: Since fprop code is only
used for bdi writeback tracking, I guess there's no good reason to make
this configurable on a per-proportion basis. Just drop this patch and
bump PROP_BATCH in the following patch and we are done. Am I missing
something?

								Honza

> > ---
> >  include/linux/flex_proportions.h |  4 +++-
> >  lib/flex_proportions.c           | 11 +++++------
> >  2 files changed, 8 insertions(+), 7 deletions(-)
> > 
> > diff --git a/include/linux/flex_proportions.h b/include/linux/flex_proportions.h
> > index 0d348e011a6e..853f4305d1b2 100644
> > --- a/include/linux/flex_proportions.h
> > +++ b/include/linux/flex_proportions.h
> > @@ -20,7 +20,7 @@
> >   */
> >  #define FPROP_FRAC_SHIFT 10
> >  #define FPROP_FRAC_BASE (1UL << FPROP_FRAC_SHIFT)
> > -
> > +#define FPROP_BATCH_SIZE (8*(1+ilog2(nr_cpu_ids)))
> >  /*
> >   * ---- Global proportion definitions ----
> >   */
> > @@ -31,6 +31,8 @@ struct fprop_global {
> >  	unsigned int period;
> >  	/* Synchronization with period transitions */
> >  	seqcount_t sequence;
> > +	/* batch size */
> > +	s32 batch_size;
> >  };
> >  
> >  int fprop_global_init(struct fprop_global *p, gfp_t gfp);
> > diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c
> > index 2cc1f94e03a1..5552523b663a 100644
> > --- a/lib/flex_proportions.c
> > +++ b/lib/flex_proportions.c
> > @@ -44,6 +44,7 @@ int fprop_global_init(struct fprop_global *p, gfp_t gfp)
> >  	if (err)
> >  		return err;
> >  	seqcount_init(&p->sequence);
> > +	p->batch_size = FPROP_BATCH_SIZE;
> >  	return 0;
> >  }
> >  
> > @@ -166,8 +167,6 @@ void fprop_fraction_single(struct fprop_global *p,
> >  /*
> >   * ---- PERCPU ----
> >   */
> > -#define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
> > -
> >  int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp)
> >  {
> >  	int err;
> > @@ -204,11 +203,11 @@ static void fprop_reflect_period_percpu(struct fprop_global *p,
> >  	if (period - pl->period < BITS_PER_LONG) {
> >  		s64 val = percpu_counter_read(&pl->events);
> >  
> > -		if (val < (nr_cpu_ids * PROP_BATCH))
> > +		if (val < (nr_cpu_ids * p->batch_size))
> >  			val = percpu_counter_sum(&pl->events);
> >  
> >  		percpu_counter_add_batch(&pl->events,
> > -			-val + (val >> (period-pl->period)), PROP_BATCH);
> > +			-val + (val >> (period-pl->period)), p->batch_size);
> >  	} else
> >  		percpu_counter_set(&pl->events, 0);
> >  	pl->period = period;
> > @@ -219,7 +218,7 @@ static void fprop_reflect_period_percpu(struct fprop_global *p,
> >  void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
> >  {
> >  	fprop_reflect_period_percpu(p, pl);
> > -	percpu_counter_add_batch(&pl->events, 1, PROP_BATCH);
> > +	percpu_counter_add_batch(&pl->events, 1, p->batch_size);
> >  	percpu_counter_add(&p->events, 1);
> >  }
> >  
> > @@ -267,6 +266,6 @@ void __fprop_inc_percpu_max(struct fprop_global *p,
> >  			return;
> >  	} else
> >  		fprop_reflect_period_percpu(p, pl);
> > -	percpu_counter_add_batch(&pl->events, 1, PROP_BATCH);
> > +	percpu_counter_add_batch(&pl->events, 1, p->batch_size);
> >  	percpu_counter_add(&p->events, 1);
> >  }
> > -- 
> > 2.7.5
> > 
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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