netdev - [net-next v6 PATCH 2/2] page_pool: help compiler remove code in case CONFIG

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Date:   Fri, 27 Dec 2019 18:13:24 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>, lirongqing@...du.com,
        linyunsheng@...wei.com,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Saeed Mahameed <saeedm@...lanox.com>, mhocko@...nel.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: [net-next v6 PATCH 2/2] page_pool: help compiler remove code in case
 CONFIG_NUMA=n

When kernel is compiled without NUMA support, then page_pool NUMA
config setting (pool->p.nid) doesn't make any practical sense. The
compiler cannot see that it can remove the code paths.

This patch avoids reading pool->p.nid setting in case of !CONFIG_NUMA,
in allocation and numa check code, which helps compiler to see the
optimisation potential. It leaves update code intact to keep API the
same.

 $ ./scripts/bloat-o-meter net/core/page_pool.o-numa-enabled \
                           net/core/page_pool.o-numa-disabled
 add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-113 (-113)
 Function                                     old     new   delta
 page_pool_create                             401     398      -3
 __page_pool_alloc_pages_slow                 439     426     -13
 page_pool_refill_alloc_cache                 425     328     -97
 Total: Before=3611, After=3498, chg -3.13%

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 net/core/page_pool.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 748f0d36f4be..28fe694f9ab2 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -113,7 +113,12 @@ static struct page *page_pool_refill_alloc_cache(struct page_pool *pool,
 	/* Softirq guarantee CPU and thus NUMA node is stable. This,
 	 * assumes CPU refilling driver RX-ring will also run RX-NAPI.
 	 */
+#ifdef CONFIG_NUMA
 	pref_nid = (pool->p.nid == NUMA_NO_NODE) ? numa_mem_id() : pool->p.nid;
+#else
+	/* Ignore pool->p.nid setting if !CONFIG_NUMA, helps compiler */
+	pref_nid = numa_mem_id(); /* will be zero like page_to_nid() */
+#endif
 
 	/* Slower-path: Get pages from locked ring queue */
 	spin_lock(&r->consumer_lock);
@@ -200,7 +205,11 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	 */
 
 	/* Cache was empty, do real allocation */
+#ifdef CONFIG_NUMA
 	page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
+#else
+	page = alloc_pages(gfp, pool->p.order);
+#endif
 	if (!page)
 		return NULL;