page_pool: Add allocation stats

Add per-pool statistics counters for the allocation path of a page pool.
These stats are incremented in softirq context, so no locking or per-cpu
variables are needed.

This code is disabled by default and a kernel config option is provided for
users who wish to enable them.

The statistics added are:
	- fast: successful fast path allocations
	- slow: slow path order-0 allocations
	- slow_high_order: slow path high order allocations
	- empty: ptr ring is empty, so a slow path allocation was forced.
	- refill: an allocation which triggered a refill of the cache
	- waive: pages obtained from the ptr ring that cannot be added to
	  the cache due to a NUMA mismatch.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/page_pool.h

@@ -84,6 +84,19 @@ struct page_pool_params {
 	void *init_arg;
 };
 
+#ifdef CONFIG_PAGE_POOL_STATS
+struct page_pool_alloc_stats {
+	u64 fast; /* fast path allocations */
+	u64 slow; /* slow-path order 0 allocations */
+	u64 slow_high_order; /* slow-path high order allocations */
+	u64 empty; /* failed refills due to empty ptr ring, forcing
+		    * slow path allocation
+		    */
+	u64 refill; /* allocations via successful refill */
+	u64 waive;  /* failed refills due to numa zone mismatch */
+};
+#endif
+
 struct page_pool {
 	struct page_pool_params p;
 
@@ -96,6 +109,11 @@ struct page_pool {
 	unsigned int frag_offset;
 	struct page *frag_page;
 	long frag_users;
+
+#ifdef CONFIG_PAGE_POOL_STATS
+	/* these stats are incremented while in softirq context */
+	struct page_pool_alloc_stats alloc_stats;
+#endif
 	u32 xdp_mem_id;
 
 	/*

net/Kconfig

@@ -434,6 +434,19 @@ config NET_DEVLINK
 config PAGE_POOL
 	bool
 
+config PAGE_POOL_STATS
+	default n
+	bool "Page pool stats"
+	depends on PAGE_POOL
+	help
+	  Enable page pool statistics to track page allocation and recycling
+	  in page pools. This option incurs additional CPU cost in allocation
+	  and recycle paths and additional memory cost to store the statistics.
+	  These statistics are only available if this option is enabled and if
+	  the driver using the page pool supports exporting this data.
+
+	  If unsure, say N.
+
 config FAILOVER
 	tristate "Generic failover module"
 	help

net/core/page_pool.c

@@ -26,6 +26,13 @@
 
 #define BIAS_MAX	LONG_MAX
 
+#ifdef CONFIG_PAGE_POOL_STATS
+/* alloc_stat_inc is intended to be used in softirq context */
+#define alloc_stat_inc(pool, __stat)	(pool->alloc_stats.__stat++)
+#else
+#define alloc_stat_inc(pool, __stat)
+#endif
+
 static int page_pool_init(struct page_pool *pool,
 			  const struct page_pool_params *params)
 {
@@ -117,8 +124,10 @@ static struct page *page_pool_refill_alloc_cache(struct page_pool *pool)
 	int pref_nid; /* preferred NUMA node */
 
 	/* Quicker fallback, avoid locks when ring is empty */
-	if (__ptr_ring_empty(r))
+	if (__ptr_ring_empty(r)) {
+		alloc_stat_inc(pool, empty);
 		return NULL;
+	}
 
 	/* Softirq guarantee CPU and thus NUMA node is stable. This,
 	 * assumes CPU refilling driver RX-ring will also run RX-NAPI.
@@ -145,14 +154,17 @@ static struct page *page_pool_refill_alloc_cache(struct page_pool *pool)
 			 * This limit stress on page buddy alloactor.
 			 */
 			page_pool_return_page(pool, page);
+			alloc_stat_inc(pool, waive);
 			page = NULL;
 			break;
 		}
 	} while (pool->alloc.count < PP_ALLOC_CACHE_REFILL);
 
 	/* Return last page */
-	if (likely(pool->alloc.count > 0))
+	if (likely(pool->alloc.count > 0)) {
 		page = pool->alloc.cache[--pool->alloc.count];
+		alloc_stat_inc(pool, refill);
+	}
 
 	return page;
 }
@@ -166,6 +178,7 @@ static struct page *__page_pool_get_cached(struct page_pool *pool)
 	if (likely(pool->alloc.count)) {
 		/* Fast-path */
 		page = pool->alloc.cache[--pool->alloc.count];
+		alloc_stat_inc(pool, fast);
 	} else {
 		page = page_pool_refill_alloc_cache(pool);
 	}
@@ -239,6 +252,7 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
 		return NULL;
 	}
 
+	alloc_stat_inc(pool, slow_high_order);
 	page_pool_set_pp_info(pool, page);
 
 	/* Track how many pages are held 'in-flight' */
@@ -293,10 +307,12 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	}
 
 	/* Return last page */
-	if (likely(pool->alloc.count > 0))
+	if (likely(pool->alloc.count > 0)) {
 		page = pool->alloc.cache[--pool->alloc.count];
-	else
+		alloc_stat_inc(pool, slow);
+	} else {
 		page = NULL;
+	}
 
 	/* When page just alloc'ed is should/must have refcnt 1. */
 	return page;