Re: [PATCH net-next 1/2] page_pool: Convert page_pool_recycle_stats to u64_stats_t.

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2025-02-22 16:13:35 [+0800], Yunsheng Lin wrote:
> > @@ -99,11 +106,19 @@ bool page_pool_get_stats(const struct page_pool *pool,
> >  		const struct page_pool_recycle_stats *pcpu =
> >  			per_cpu_ptr(pool->recycle_stats, cpu);
> >  
> > -		stats->recycle_stats.cached += pcpu->cached;
> > -		stats->recycle_stats.cache_full += pcpu->cache_full;
> > -		stats->recycle_stats.ring += pcpu->ring;
> > -		stats->recycle_stats.ring_full += pcpu->ring_full;
> > -		stats->recycle_stats.released_refcnt += pcpu->released_refcnt;
> > +		do {
> > +			start = u64_stats_fetch_begin(&pcpu->syncp);
> > +			u64_stats_add(&stats->recycle_stats.cached,
> > +				      u64_stats_read(&pcpu->cached));
> > +			u64_stats_add(&stats->recycle_stats.cache_full,
> > +				      u64_stats_read(&pcpu->cache_full));
> > +			u64_stats_add(&stats->recycle_stats.ring,
> > +				      u64_stats_read(&pcpu->ring));
> > +			u64_stats_add(&stats->recycle_stats.ring_full,
> > +				      u64_stats_read(&pcpu->ring_full));
> > +			u64_stats_add(&stats->recycle_stats.released_refcnt,
> > +				      u64_stats_read(&pcpu->released_refcnt));
> 
> It seems the above u64_stats_add() may be called more than one time
> if the below u64_stats_fetch_retry() returns true, which might mean
> the stats is added more than it is needed.
> 
> It seems more correct to me that pool->alloc_stats is read into a
> local varible in the while loop and then do the addition outside
> the while loop?

indeed, indeed, what was I thinking…

> 
> > +		} while (u64_stats_fetch_retry(&pcpu->syncp, start));
> >  	}
> >  
> >  	return true;

Sebastian