Subject: Re: [RFC net-next] net: page_pool: fix recycle stats for percpu page_pool allocator

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Wed, 14 Feb 2024 22:42:45 +0100

Lorenzo Bianconi <[email-masked]> writes:

> Use global page_pool_recycle_stats percpu counter for percpu page_pool
> allocator.
>
> Signed-off-by: Lorenzo Bianconi <[email-masked]>

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 <[email-masked]>

> ---
>  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?

>  /* 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