netdev - Re: [RFC net-next] net: page_pool: fix recycle stats for percpu page

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Message-ID: <Zc1CrXyLYRR2w9RX@lore-desk>
Date: Wed, 14 Feb 2024 23:46:05 +0100
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: Toke Høiland-Jørgensen <toke@...hat.com>
Cc: netdev@...r.kernel.org, lorenzo.bianconi@...hat.com, kuba@...nel.org,
	davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
	hawk@...nel.org, ilias.apalodimas@...aro.org,
	linyunsheng@...wei.com
Subject: Re: [RFC net-next] net: page_pool: fix recycle stats for percpu
 page_pool allocator

> Lorenzo Bianconi <lorenzo@...nel.org> writes:
> 
> > Use global page_pool_recycle_stats percpu counter for percpu page_pool
> > allocator.
> >
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> 
> Neat trick with just referencing the pointer to the global object inside
> the page_pool. With just a few nits below:
> 
> Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>
> 
> > ---
> >  net/core/page_pool.c | 18 +++++++++++++-----
> >  1 file changed, 13 insertions(+), 5 deletions(-)
> >
> > diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> > index 6e0753e6a95b..1bb83b6e7a61 100644
> > --- a/net/core/page_pool.c
> > +++ b/net/core/page_pool.c
> > @@ -31,6 +31,8 @@
> >  #define BIAS_MAX	(LONG_MAX >> 1)
> >  
> >  #ifdef CONFIG_PAGE_POOL_STATS
> > +static DEFINE_PER_CPU(struct page_pool_recycle_stats, pp_recycle_stats);
> 
> Should we call this pp_system_recycle_stats to be consistent with the
> naming of the other global variable?

ack, I agree.

> 
> >  /* alloc_stat_inc is intended to be used in softirq context */
> >  #define alloc_stat_inc(pool, __stat)	(pool->alloc_stats.__stat++)
> >  /* recycle_stat_inc is safe to use when preemption is possible. */
> > @@ -220,14 +222,19 @@ static int page_pool_init(struct page_pool *pool,
> >  	pool->has_init_callback = !!pool->slow.init_callback;
> >  
> >  #ifdef CONFIG_PAGE_POOL_STATS
> > -	pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
> > -	if (!pool->recycle_stats)
> > -		return -ENOMEM;
> > +	if (cpuid < 0) {
> > +		pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
> > +		if (!pool->recycle_stats)
> > +			return -ENOMEM;
> > +	} else {
> 
> Maybe add a short comment here to explain what's going on? Something
> like:
> 
> /* When a cpuid is supplied, we're initialising the percpu system page pool
>  * instance, so use a singular stats object instead of allocating a
>  * separate percpu variable for each (also percpu) page pool instance.
>  */
> 
> -Toke
> 

sure, I will add it.

Regards,
Lorenzo

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